To prepare crust, lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, granulated sugar, baking powder, and 1/4 teaspoon salt in a bowl. Add milk and butter; toss with a fork until moist.
Press mixture gently into a 4-inch circle on heavy-duty plastic wrap; cover with additional plastic wrap. Roll dough, still covered, to an 11-inch circle. Freeze 10 minutes or until plastic wrap can be easily removed.
Remove 1 sheet of plastic wrap; fit dough into a 9-inch pie plate coated with cooking spray. Remove top sheet of plastic wrap. Fold edges under; flute.
Preheat oven to 350°.
To prepare the filling, beat the egg and the next 4 ingredients (egg through 1/4 teaspoon salt) at medium speed of a mixer until well-blended. Stir in the pecan halves and the vanilla extract. Pour the mixture into the prepared crust. Bake the pie at 350° for 20 minutes, then cover with foil. Bake the pie an additional 20 minutes or until a knife inserted 1 inch from the edge comes out clean. Do not overbake. Cool pie on a wire rack.