IT took Elise Ambrose two months to gain 30 pounds, selling her chocolate chip cookies while eating them, too. It took Julie Ward, her partner, 21 years to conquer her addiction to T.H.O.S.E. cookies, but then Ward grew up on them--they're an adaptation of her grandmother's recipe.

"I love those cookies," Ambrose said, admitting that before her recent diet she would make a home batch of seven or eight dozen and polish them off over a weekend while doing the company's books. "You'd think that after all this time, I'd be tired of them. But I could eat as many today as I could a year ago. I'm thinking of having myself hypnotized," she added, only half jokingly.

Judging by the recent surge in sales to grocery stores and downtown luncheon carryouts, Ambrose is not the only person eating the distinctive chocolate chip cookies and brownies she and Ward bake each weekday afternoon in a rented Georgetown kitchen. Their operation, dubbed The House of Sensuous Eats, has grown from weekly deliveries of 100 dozen cookies to 600 dozen cookies and 800 brownies. They say they could sell dozens more if they had kitchen help--something they've begun to consider seriously due to the anticipated May 1 opening of their cookie shop in Manassas.

"I remember saying to myself, why would I want to go into the chocolate chip cookie business?" said 26-year-old Ambrose, who worked as manager of an office furniture warehouse when Ward offered her a kitchen partnership 13 months ago. "But then I realized Julie had been thinking about this for a long, long time."

It took four months before they delivered the first cookies to the first carryouts. In addition to finding a kitchen where they would do their baking, there were health department forms and paperwork to sift through, labels to design, a small home recipe to revise, and the naming of the cookie company. They decided on The House of Super Eats (later changed to Sensuous) early on, working backward from the acronym T.H.O.S.E.--since family and friends kept asking for more of "those" cookies. There would also be a new life style to adjust to, becoming vagabonds of a sort, living from the trunk of a car between their own homes and those of friends and family who live closer to their M Street kitchen.

But you can't market a cookie without designing its cover and you can't sell it without meeting health department regulations. So Ward, a design major at the University of Maryland, sat down at the drawing board and came up with the packaging: "I wanted a handmade look; after all, the cookies are handmade." So she chose the bold, round red lettering and smooth lines. Health department requirements were a major concern; they had to get not only the name on the label but also the ingredients, the package weight and still leave space to stamp an expiration date, all in a 2 1/2-inch space.

All the while, they were baking test batches and enlarging the recipe--keeping in mind the taste and texture of the original cookie, while at the same time learning how to bake with a large commercial oven. It took, Ambrose said, not only hundreds of pounds of ingredients, but many understanding friends who would take off their hands the thousands of cookies resulting from each test batch. "One day they'd be too thin, the next too thick," Ward said.

It would be nearly impossible, they decided, to transport the original lace cookie, which was almost transparent, without losing a large percentage to breakage. So they came up with a less delicate, slightly chewy cookie.

Margarine, they learned, prevents the cookies from sticking, so they changed the fat in the recipe from all butter to a combination of butter and margarine. "It's also cheaper," added Ambrose. In the early days they did their shopping at the Georgetown Safeway. They've since discovered a Jessup, Md., wholesaler where they buy sugar and chocolate chips by the 100-pound bag. Flour, they say, is a less important ingredient. "We could add pounds and pounds of flour to that batter and still be as good as most average chocolate chip cookies, but that's why ours are so much better," Ambrose said, adding, "that's not the only secret, but one of them."

Ambrose watches the oven because Ward burns the cookies; Ward is the expert batter-beater. Just one minute of overbeating can ruin a 50-pound batch of cookies, Ward said--a little over half an afternoon's baking. "It works out," Ambrose said. "What we're wondering is how are we ever going to train anybody to do this as well as we do?"

As they pack their belongings and begin the move into their new cookie shop, located next door to a chocolate supply shop in Manassas, staff expansion is foremost on their minds. They've added oatmeal raisin and peanut butter chocolate chip to their cookie selection, and mint chocolate, butterscotch and toffee to the brownie selection. They plan to continue morning deliveries to four Lunch Box locations, Pasta Inc., Scheele's Market, Neam's Market, Wagshal's Delicatessen, Georgetown Haagen-Dazs, and Safeway in McLean and Georgetown. And in addition to their regular afternoon routine of handling phone orders, buying supplies, and baking and packaging cookies for the next day's deliveries, they'll add the task of selling over-the-counter cookies.

Why Manassas? "Because it's growing so fast out there," Ambrose said. "Besides, we don't have the capital to put one down on K Street." She added that financial backing is coming from "people who have watched us grow."

The company, she said, has always operated in the black. They take enough of the profits to pay their rent and put the rest back into the new shop. "We don't really care," Ambrose said. "I can go a year without making much money, knowing how much money we're going to make in three years."