Make Dough: Combine butter and cream cheese in a mixer. Add flour and mix on low, then medium, until dough is well incorporated.
Prep Pan (The Hack): Cut 5 1/2-inch narrow strips of parchment paper. Spray a 48-cup mini muffin pan with baking spray. Place one strip in each cavity to create lifting handles.
Shape: Scoop small balls of dough into each cup. Dip a tassie tamper (or back of a spoon) into powdered sugar and press the dough to form a cup shape against the sides of the tin.
Make Filling: Whisk together sugars, salt, and spices. Whisk in pumpkin, evaporated milk, egg, and vanilla until smooth.
Fill: Spoon pumpkin mixture into the dough cups, filling only 3/4 full. (Do not overfill!).
Bake: Bake at 325°F (160°C) for 16-20 minutes. Check at 10 minutes. Remove when crust edges are very light brown and filling is set.
Cool: Let cool in pan for 10-15 minutes. Use parchment strips to lift tassies onto a wire rack to cool completely.
Serve: Top with homemade whipped cream.