Prepare Snickerdoodle Topping. Preheat oven to 350 degrees F. Coat a 2-quart baking dish with cooking spray; set aside.
For filling, in a large bowl combine eggs, pumpkin, evaporated milk, the 1/2 cup granulated sugar, the brown sugar, flour, pumpkin pie spice, and salt. Whisk until thoroughly combined. Pour into prepared baking dish.
Combine the 1/4 cup granulated sugar and the cinnamon. Shape Snickerdoodle Topping into 16 balls. Roll balls in the cinnamon-sugar. Press balls to slightly flatten to 1 3/4-inch-diameter rounds. Place over pumpkin filling.
Bake 35 to 40 minutes or until filling is set, edges begin to pull away from dish, and a knife inserted near the center comes out clean. Cool 15 minutes on a wire rack. Serve warm and, if desired, with whipped cream.
In a medium bowl beat butter with a mixer on medium for 30 seconds. Add sugar, baking powder, cream of tartar, and salt. Beat until combined, scraping bowl as needed. Beat in egg. Beat in flour just until combined. Cover and chill dough 1 hour or until easy to handle.