My husband has a theory: When you decide to buy a new car, everywhere you look, you see that particular model. I don’t know if that’s true, but I can say with confidence that once you make a few hundred pies, everything begins to look like a pie. And that is how I came to define a knish as a kinda-pie, a pastry wrapped around filling. In fact, I put empanadas, calzones and samosas in the same category. It’s all pie to me. And every iteration is delicious.

The deeper my dive into pie — using this new, expanded definition — the more I’ve come to understand pie can be a way to use up extra food. What home cook doesn’t appreciate a new and creative way to reimagine those few ounces of leftover roast chicken, a meager bowl of last night’s chickpeas, or the remaining blueberries languishing in the refrigerator? With flaky pastry, from pie dough to phyllo, puff pastry to strudel, tuck in those bits and bobs and feed the family one more time, in a new and reimagined form.

A knish (the K is voiced: ka-nish) is a classic filled pastry. While potato knishes are most common, there are other fillings, too, and the Internet shows a few versions of the pastry. When I decided to include a recipe in my new book, “When Pies Fly” (Grand Central Publishing, 2019), I searched through the cookbooks my grandmothers passed down to me — a Hadassah collection that was a gift to my great-grandmother Agatha and “The New Settlement Cook Book,” inscribed to Mary with love from Aunt Sophie of Yum-Yum Coffee Cake fame. But it was in Mary’s recipe cards that I found inspiration and a version of the recipe printed here.

Mary was Lithuanian by birth, and I believe this method, and most particularly the dough, was a product of that upbringing. A knish recipe often calls for dough that is both dairy- and meat-free, avoiding butter or animal fat, and using oil instead, which permits a kosher household (where dairy and meat are not mixed) to stuff the pastry with either filling. The recipe card had the rough outlines of the dough with a potato filling; admittedly, I added some personal flourishes, such as fresh herbs and creme fraiche. My grandmother did not know from creme fraiche.

The dough, whisked with a fork, comes together quickly, and I’ve learned to love the kneading, feeling the dough turn silky smooth under my hands. A required one-hour rest for the dough allows plenty of time to stir together the filling, particularly if reimagining last night’s leftovers. Here, I’ve taken mashed potatoes, generously seasoned and studded with fresh chives. Whatever filling you choose, it must have a strong flavor to stand out when surrounded by dough, so use salt and pepper liberally, and then taste.

The dough is reminiscent of strudel dough, but is even more elastic. It can be pulled to size like strudel, but it’s bouncy and resistant, so a rolling pin is easier. I mark off a 12-by-12-inch space on the counter using painters’ or masking tape, so I can aim for the correct size and shape. It will seem as if the dough will not fill that space, but it will, and it will be whisper thin. There is no need to flour the counter; this oily dough will not stick. I place a log of filling near the edge of the square and roll it up like a fat cigar, pinching the edge to seal.

Shaping the knish is like forming sausage; use a sharp knife or scissors to snip the long cylinder into six even pieces. Shape the knish by lifting and pinching together the edges of the dough. I like to leave the tops open so the filling is exposed, but it’s also possible to crimp the top closed. Be careful not to compact the potato filling too much as it expands during baking, and will either volcano out of the top or bust through the sides.

I love to bring these knishes to a party. They’re surprising, light, crispy and satisfying. Easy to serve as a finger food, these knishes will put to rest any thoughts of the belly bombs that lurk in deli cases. Make a double recipe and stash some away for brunch or an afternoon snack. I have them ready for the upcoming holidays, perfect to take along for Rosh Hashanah lunch or for breaking the fast on Yom Kippur. Just tell the hosts you’ll be bringing pie.

Barrow is a Washington cookbook author; her new book, “When Pies Fly” (Grand Central Publishing) is out today. She’ll join Wednesday’s Free Range chat at noon: live.washingtonpost.com.

Classic Potato Knishes

Makes 18 knishes

The pastry dough will look odd and lumpy at first, but after a rest it comes together in a silky, stretchy, easy-to-roll dough. Do not refrigerate or freeze the dough. Once cold, it is impossible to work. Let the filling cool completely before forming the knishes. It is possible to make the dough in a stand mixer using the dough hook, but it is not necessary.

MAKE AHEAD: The dough needs to rest for 1 hour before rolling. The filling needs at least 1 hour to cool, and may be made 1 day ahead. Knishes may be formed and frozen for up to 3 months, before or after baking.

From Bring It! columnist Cathy Barrow.

Ingredients

For the dough

½ cup (120 milliliters) canola oil, or another neutral oil

¼ to ⅓ cup (60 to 80 milliliters) cool water

1 large egg

1 teaspoon white vinegar

½ teaspoon kosher salt

Scant 2½ cups (300 grams) flour

1 teaspoon baking powder

For the filling

1¾ pounds (800 grams) russet potatoes (about 4 medium)

¾ cup (180 grams) creme fraiche or sour cream

4 tablespoons (56 grams) unsalted butter

¼ cup (15 grams) snipped chives

¼ cup (15 grams) chopped fresh flat-leaf parsley

1 teaspoon kosher salt

½ teaspoon freshly ground black pepper

For the egg wash

1 large egg

1 tablespoon cool water

¼ teaspoon kosher salt

Steps

Make the dough: In a medium bowl, whisk together the oil, ¼ cup water, 1 egg, the vinegar and salt. In a large bowl, combine the flour and baking powder. Make a well in the dry ingredients and pour in the liquid ingredients. Using a fork, stir until a rough ball is formed. With your hands, working in the bowl, knead the ball of dough until smooth and elastic, about 8 minutes. Cover the bowl and let the dough rest for 1 hour.

Make the filling: Preheat the oven to 350 degrees with the rack in the middle.

Scrub the potatoes and pierce them with a knife in a few places. Bake the potatoes directly on the oven rack for 55 to 60 minutes, until easily pierced with a fork.

Remove the potatoes from the oven and, holding a hot potato with a dry towel, make a vertical slit across the top. Squeeze at both ends to open the potato and release the steam. Using a fork, fluff the potato, then scrape it out of the peel into a large bowl. Repeat with the remaining potatoes.

Add the creme fraiche, butter, chives, parsley, salt and pepper to the potatoes and stir and mash with a fork, a potato masher, or a sturdy whisk until the potatoes are smooth and creamy. Cool completely.

Assemble the knishes: Preheat the oven to 375 degrees and line a baking sheet with parchment paper.

Knead the dough, incorporating back into the dough any oil that pools at the bottom of the bowl. Divide the dough into three pieces; cover two with plastic wrap while working with the first.

Roll out one section of dough into a whisper-thin 12-by-12-inch square. The dough will want to snap back, but use a firm hand to stretch it to size.

Leaving a border of about 1 inch, place 1 cup of the filling along the length of the dough in a long log. Lift the dough edge closest to the filling and stretch it up and over the filling snugly. Don’t fret if the dough tears; just roll it up. You should have a 12-inch log of dough filled with potato.

Place the log parallel to the counter edge and use the side of your hand to indent the roll in 5 places, measuring for 6 knishes, each about 2 inches long. Grasping the log, form each knish by slightly twisting at the indents in opposite directions for 6 pudgy little knishes.

Using a sharp knife, scissors or a pizza wheel, cut between each knish. One end of the knish will inevitably have more dough -- that’s the bottom. The other end will have exposed filling. You can either pull the dough up and around the filling to close the knish, pinching the dough together, or leave it open to expose the filling.

Work this way to form 6 pastries, setting each finished knish on the baking sheet. Repeat with the remaining two pieces of dough. You should have 18 knishes on the baking sheet.

In a small bowl, lightly beat the egg with the water and salt until combined. Brush the sides of the knishes with the egg wash and bake for 30 minutes, until deeply golden brown. Transfer to a wire rack and let cool slightly before serving.

Nutrition | Per knish: 220 calories, 3 g protein, 23 g carbohydrates, 13 g fat, 5 g saturated fat, 30 mg cholesterol, 130 mg sodium, 1 g dietary fiber, 0 g sugar

Recipe tested by Cathy Barrow; email questions to food@washpost.com

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