Preheat conventional oven to 400°F. Cut squash in half and remove seeds.
Roast halved squash facedown on sheet pans until tender when pierced with a fork and skin is beginning to brown slightly, about 45 minutes.
Reduce heat in convection oven to 350°F or conventional oven to 375°F. Coat a full 2-inch hotel pan with cooking spray.
Scoop squash flesh from the skin to a large bowl and mash (or purée in batches in a food processor until smooth).
Beat eggs in a mixing bowl. Add the eggs, sugar (or maple syrup), butter, flour, baking powder and vanilla to the squash; mix well. Transfer to the prepared pan.
Bake until the top is set and lightly browned, 30 to 35 minutes.
