Melissa Walnock loves playing with food. The pastry chef and lecturing instructor at the Culinary Institute of America, Hyde Park, N.Y., enjoys pairing familiar ingredients with something a little unexpected in the desserts she creates. Corn is turned into corn mousse served with fresh berries and tarragon. Blueberry sorbet is made with a bit of green cardamom. The most unusual, though, is her take on a strawberry shortcake: shortbread, strawberry “spheres” (strawberries pickled with…