Remove ice cream to a large bowl. In a food processor combine flour, cold butter cubes and vanilla. Pulse until mixture looks like a crumbled course meal. Stir into ice cream in bowl, mix with a spoon then with hands gently knead cold dough until it just starts to clump up. Drop clumps of dough evenly into prepared pan. Bake about 20 minutes until light golden brown. Cool on a rack 15 minutes then lift out carefully using the parchment, cake can break if your not careful. Finish cooling and cut into sqares