Preheat oven to 325 degrees and line a 9x9 pan with parchment paper and spray with non-stick cooking spray for easy removal.
After butter is melted and cooled, warm the milk of choice until it is lukewarm and set it aside, about 40 seconds worth.
Whip the egg whites with the cream of tartar until stiff peaks form and set aside.
Beat the egg yolks and the powdered sugar until light yellow.
Add the melted butter, vanilla, cinnamon, ginger, and nutmeg and mix until combined.
Add the flour and mix together.
Add in the pumpkin and ½ cup of milk of choice. and continue mixing together, scraping down sides of bowl until combined well.
Place mixer on the lowest speed, and add the remaining milk gradually until combined.
Gently fold in/stir in the egg whites by hand.
Pour into prepared pan.
Bake for 55-65 minutes.
Cake will still be jiggly because it is custard but it shouldn't be runny.
Allow the cake to cool completely before cutting.
Add powdered sugar for sprinkling on top and some whipped topping! My husband likes to warm up his magic cake in the microwave and then adds the whipped cream. Outstanding!