Pistachio, Lemon, and Vanilla Shortbread

Name: Pistachio, Lemon, and Vanilla Shortbread
Yield: Makes 24 cookies
Ingredients: 1 1/2 cups all purpose flour; 1/2 cup sugar; 1/2 cup semolina flour*; 1 cup (2 sticks) chilled unsalted butter, cut into 1/2-inch cubes; 1 1/2 teaspoons grated lemon peel; 1 teaspoon vanilla extract; 1 cup shelled natural pistachios (about 4 ounces), coarsely chopped