01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish.
02 - In a medium bowl, whisk together all-purpose flour, pumpkin pie spice, baking powder, and salt.
03 - In a large bowl, beat egg yolks with 3/4 cup sugar until pale and thick. Incorporate pumpkin puree, whole milk, and vanilla extract.
04 - Gently fold dry mixture into the egg yolk batter until just combined.
05 - In a separate clean bowl, beat egg whites until soft peaks form. Gradually add remaining 1/4 cup sugar and continue to beat until stiff peaks develop.
06 - Carefully fold the whipped egg whites into the batter in three additions, preserving as much volume as possible.
07 - Transfer batter to the prepared baking dish and smooth the top. Bake for 30–35 minutes, or until a toothpick inserted in the center emerges cleanly. Let cool in pan for 15 minutes.
08 - While the cake cools, whisk together sweetened condensed milk, evaporated milk, whole milk, and ground cinnamon in a bowl.
09 - Poke holes across the surface of the warm cake using a fork or skewer. Slowly and evenly pour milk mixture over the entire cake. Allow to reach room temperature, then refrigerate for at least 4 hours or overnight.
10 - Shortly before serving, whip heavy cream with powdered sugar and vanilla extract until soft peaks form.
11 - Spread whipped cream over the chilled cake. Dust lightly with ground cinnamon or pumpkin pie spice. Slice and serve.