Ingredients

• 1 tablespoon white sugar, or as needed
• 1 butternut squash, halved and seeded
• 1/4 cup all-purpose flour
• 1/2 teaspoon baking powder
• 1/4 teaspoon salt
• 1/2 cup unsalted butter at room temperature
• 1/4 cup white sugar
• 1/4 cup brown sugar
• 1 teaspoon vanilla extract
• 1/2 teaspoon ground cinnamon
• 1/4 teaspoon ground nutmeg
• 3 eggs at room temperature, separated

Instructions

1. Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper. Lightly butter a souffle or ceramic baking dish and sprinkle 1 tablespoon white sugar over butter, tapping excess sugar out of dish. Store buttered and sugared dish in the refrigerator.
2. Place butternut squash, cut-side down, onto the prepared baking sheet.
3. Bake in the preheated oven until very soft, 1 to 1 1/2 hours. Allow squash to cool to room temperature.
4. Sift flour, baking powder, and salt together in a bowl.
5. Scrape flesh from butternut squash into a in a food processor until smooth. Add flour mixture, 1/4 cup white sugar, brown sugar, vanilla extract, cinnamon, and nutmeg and process until smooth. Add egg yolks, 1 at a time, to squash mixture while continually processing.
6. Beat egg whites in a bowl using an electric mixer until stiff peaks form; fold into squash mixture. Pour mixture into the chilled dish.
7. Bake in the preheated oven until browned and top springs back after pressing, about 1 hour.