Begin by ensuring all your ingredients for the Pumpkin Magic Custard Cake are at room temperature. Preheat your oven to 325°F (165°C) and line an 8x8 or 9x9-inch baking pan with parchment paper.

In a small saucepan, gently heat the whole milk over low heat until it’s lukewarm, stirring occasionally. Set it aside to cool slightly.

Whip the separated egg whites in a clean bowl until soft peaks form. Add the cream of tartar and beat until stiff peaks form, about 3-5 minutes.

Melt the unsalted butter and allow it to cool. In a separate bowl, beat the egg yolks with powdered sugar until pale and fluffy. Add in vanilla, cinnamon, pumpkin pie spice, and melted butter, mixing until combined.

Whisk in the pumpkin puree until smooth, followed by the lukewarm milk. The batter will be thin.

Gradually pour in the remainder of the milk and give the batter a final gentle stir.

Carefully fold the whipped egg whites into the batter using a spatula, making sure to leave some lumps.

Pour the prepared batter into your lined baking pan. Bake for 60-65 minutes, until the top appears golden and a slight jiggle remains in the center.

Allow the cake to cool completely in the pan on a wire rack for about an hour before refrigerating for several hours or overnight.

Slice the chilled cake into squares for serving, optionally dusting with powdered sugar or cinnamon.