In a food processor, pulse together the flour and cornmeal to blend. Cut the butter into 9 pieces and add to the food processor. Pulse until the butter is blended into the dry ingredients. Transfer the mixture to a bowl and mix in the currants or blueberries.

Beat the eggs, lemon zest if using, vanilla, and two tablespoons water into the dry ingredients. Divide the dough into 3 parts. Place the pieces of dough on a non-stick baking sheet. Shape each piece into a long rounded-top, flattened log, 2-1/2-inches x 8-inches x 1-inch.

Bake for about 20 minutes, until the dough is a light gold. Let cool 5minutes.

Cut each log diagonally into 3/4-inch slices. Place the slices, cut side down, on the baking sheet. Bake the biscotti 5 minutes. Turn them over, and bake 5 minutes longer, until they are firm. Transfer the cookies to a rack and cool completely. Store the biscotti in a tightly covered tin. They will keep 1 to 2 weeks.

Diabetic Exchanges:
1 Starch; 1/2 Fat.