Welcome back to our series Market Fresh, in which we take a look at one ingredient that's showing up in the city's Greenmarkets right now and tell you what to do with it. Last week, we looked at corn, and today we're (not) cooking with heirloom tomatoes.

Heirloom tomatoes, named as such because they're breeds that have existed without genetic modification for decades, are a fleeting treat of summer. They come in a fantastic array of shapes, sizes, and colors, in varieties like brandywine, Cherokee purple, and green zebra. Heirloom tomatoes tend to have a deeper, more intense flavor than their commercially produced, uniform-looking counterparts, and they're best enjoyed as close to raw as possible. We spoke to chef Jake Klein, of Rockefeller Plaza's Morrell Wine Bar & Cafe, to find out what he does with heirlooms.

“There’s a lot of talk these days about mass-farming, genetically modified crops, and food additives, but the heirloom tomato is as nature intended, a great way to represent what back-to-basics farming can bring," Klein says. "Each variety has its own flavor profile, its own different texture and level of sweetness, as nature intended. There's an element of surprise with colorful heirlooms—who would have thought that a striped green tomato would be so sweet and luscious? The height of the season in New York is short, so we have to take full advantage and incorporate the tomatoes into as many dishes as possible, preferably in their purest form—with light seasoning, and a drizzle of oil.”

Morrell Wine Bar & Cafe's Jake Klein's Heirloom Tomato Salad with Buffalo Mozzarella and Black Sesame Puree
Serves 8 as an appetizer or 4 as an entrée

4 lbs. mixed heirloom tomatoes
2 lbs. high-quality buffalo mozzarella
2 spring onions, thinly sliced
4 mint leaves thinly sliced
2 tsp. flat leaf parsley, thinly sliced
Half lemon, juiced
4 tsp. black sesame puree (available at most Japanese markets, or substitute 2 tsp. toasted sesame oil)
2 tbs. black truffle puree (optional; or substitute high-quality olive oil)

Cut the tomatoes and cheese into similarly sized wedges.  In a nonreactive mixing bowl combine tomatoes, mozzarella, onions, mint, parsley, and lemon juice.  Gently toss the ingredients until well mixed and season with salt to taste.  In a separate bowl, whisk together the sesame and truffle purees, and set aside.  (If you are using sesame oil, add the 2 tsp. to the tomatoes and mix one 1 tbs. vegetable oil into truffle puree in a separate bowl and set aside)

Divide the tomatoes evenly among serving plates. Using a spoon, draw a circle of the black sesame and truffle mixture (or the truffle puree and oil) around the tomato salad on each plate. Serve immediately.