Preheat oven to 375 degrees F (190 degrees C). Grease an 8-inch square baking dish.
Stir milk, sugar, and butter together in a saucepan over medium-high heat until butter and sugar melt, 1 to 2 minutes.
Mix milk mixture and pumpkin puree together in a bowl. Add cornmeal into pumpkin mixture 1/2 cup at a time, stirring batter well after each addition. Stir egg yolks and salt into batter.
Beat egg whites in a glass or metal bowl until stiff peaks form. Lift your beater or whisk straight up: the tip of the peak formed by the egg whites will form sharp peaks. Fold egg whites into batter. Pour batter into prepared baking dish.
Bake in the preheated oven until a toothpick inserted into the center of the cornbread comes out clean, about 35 minutes.