2 cups lukewarm milk
1 cup all-purpose flour
3/4 cup sugar
1/2 cup (1 stick) unsalted butter, melted and cooled
1/2 cup banana, mashed
4 large eggs, separated, room temperature
3 tablespoons brown sugar
1 teaspoon vanilla extract
1/2 teaspoon ground cinnamon
1 pinch nutmeg
Powdered sugar, garnish
Preheat oven to 325º F and line an 8×8-inch baking dish with parchment paper, or grease with non-stick spray.
In a medium bowl or mixer, beat egg whites until stiff peaks form. Set aside until ready to use.
In a separate large bowl or mixer, beat egg yolks, sugars (white and brown) and vanilla extract until ribbony and lightened in color.
Mix in melted (and slightly cooled) butter and mashed banana until incorporated, then add in flour, cinnamon and nutmeg until just combined.
Beat in milk until mixture is smooth, then, working in batches, fold in egg whites.
Pour batter into prepared baking dish and place in oven.
Bake for 45-60 minutes, or until top is golden brown and center jiggles just slightly. Tent with foil, if necessary.
Once center is just set, remove from oven and let cool, then chill until set. Dust with powdered sugar, slice into squares and enjoy!