Cream the butter and vanilla until light and fluffy.

Sift together the flour, powdered sugar, cornstarch, salt, and cream of tartar in a separate bowl.

Gradually add the dry ingredients to the creamed butter mixture, mixing until just combined.

Press the dough into a greased 8 x 8-inch pan.

Score the dough with a fork to create a crisscross design.

Bake in a preheated oven until lightly browned around the edges.