Ice cream and fresh fruit, together or separately, are among the great fleeting joys of summertime eating, and some would say that the unadorned product -- plain vanilla ice cream in a bowl with plain, perfect strawberries, for instance -- is perfection itself.

But there are others, always, who want to improve on the original. Some even want to outsmart Mother Nature.

First, on the subject of outsmarting Mother Nature:

Fresh fruit, set aside with quantities of sugar and (usually) some kind of alcohol, will eventually metamorphose into something quite different and wonderful. It's called tutti-frutti, rumtopf or brandy pot, and it's a way of making summer last until winter.

The idea is that, beginning with strawberries in June and adding other fruits as they come into season, you mix fruit, sugar and rum, brandy or other alcohol, and set it aside covered to macerate. As you add other fruits, you also add more sugar and alcohol. Most recipes advise a further period of maceration after the last fruit has been added in the fall, and a serving date of any time from the winter holidays to Mardi Gras.

You should try to find very fresh, unblemished fruit for your rumtopf, and preferably fruit that you know has not been sprayed. Jane Grigson, in her "Jane Grigson's Fruit Book" (Atheneum, 1982), suggests that chemical treatment of fruit can subvert the fermentation process and cause rumtopf to spoil and get moldy.

One thing you'll certainly need for your concoction is some kind of crockery pot, and you'll also need something to cover it with. The plain, cylindrical crockery pots of various sizes found in hardware stores will do just fine. Or you can use a more beautiful crock, such as those made especially for preserving fruit by Maryland potter Mary Bowron.

Bowron's pots are covered only by a piece of cheesecloth secured with twine, which will keep out bugs and dust, but a plate can be put over the pot if your recipe calls for a heavier cover.

Different recipes have different requirements, some calling for cool temperatures, some for room temperature, some for heavy covers, some for any kind of cover at all. In other words, there is more than one way to make these concoctions.

One friend made her "rumtopf" completely by accident. She had too many blackberries and not enough time, so she threw the fruit, which she had picked herself from a local orchard, along with quantities of sugar, into a crock. She covered it and let it sit on her kitchen counter. Soon she had slightly fermented blackberries similar to brandied blackberries, then stronger-tasting fruit. She ate the blackberries every which way, including as a topping for yogurt and ice cream, enjoying the differences in flavor as the fruit matured.

After three years on her kitchen counter (in a lovely handmade crock), her blackberry excess had turned into a perfectly clear and absolutely delicious blackberry "brandy," a serendipitous liqueur that astounded everybody, including her friend the wine snob.

Why didn't she die or get sick? Because, according to Dr. Doug Archer of the Food and Drug Administration, sugar ties up the water that bacteria need to grow. Naturally occurring yeasts then are able to take over and produce acid (and then alcohol), which further inhibits bacterial growth.

For information on more conventional ways of preserving fruits with alcohol, including some nice recipes, take a look at "Preserving," one in "The Good Cook" series from Time-Life Books.

One of the ways to use brandied fruit is with ice cream, which brings us to ways of improving on that substance.

Even unexciting, store-bought ice cream becomes a little less boring if you shape it in a mold before serving it. But homemade sherbets, parfaits and ice creams, on the other hand, can become positively exquisite.

One of the advantages of an ice cream mold -- which can be anything from a plain metal bowl to the elaborately detailed molds made especially for the purpose -- is that you can combine flavors, which has an enhancing effect not only on the taste of the finished product but also on how it looks.

Line a decorated, square mold with a layer of good vanilla ice cream, for instance, then fill it with chocolate ice cream or, better, a flavored parfait (a parfait is a heavenly rich custard that is usually beaten well before freezing, but frozen without agitation). Decorate the top with rosettes of whipped cream, and serve it sliced into wedges, which will reveal the pattern of the two flavors.

The best ice cream molds are of metal, which doesn't crack with constant temperature changes as plastic does, and conducts heat better, which means it will respond more quickly when you dip it into hot water to unmold. You can use any metal container, and you can use your imagination. One French book details instructions for making a family of ice cream mushrooms, for instance. Individual-sized molds in animal shapes are terrific for children's parties.

For ideas and recipes, see Gaston Leno tre's mouth-watering exposition on the subject called "Leno tre's Ice Creams and Candies" (Barron's, 1979).