THE MOTHER OF ALL BUTTER COOKIES

Steps:

• Preheat oven to 375 degrees. Combine flour, cornstarch, sugar and salt in a food processor, and pulse once or twice. Add butter, and pulse 10 or 20 times, until butter and flour are well combined. Add vanilla and egg and pulse 3 or 4 times. Add about half the milk and pulse 2 or 3 times. Add the remaining milk a little at a time, pulsing once or twice after each addition, until the dough holds together in a sticky mass.
• Remove the dough from the machine to one or more bowls. Make cookies as described in Step 3, or make any of the variations below.
• To make cookies, drop rounded teaspoons of dough (you can make the cookies larger or smaller, if you like) onto a nonstick baking sheet, a sheet lined with parchment paper or a lightly buttered sheet. If you want flat cookies, press the balls down a bit with your fingers or the back of a spatula or wooden spoon. Bake 11 minutes, or until the cookies are done as you like them. Cool on a rack, then store, if necessary, in a covered container.