Preheat oven to 375 degrees Fahrenheit.

Combine egg yolks and brown sugar.

Beat until the mixture forms stiff peaks.

Stir in squash puree and set aside.

In a small bowl, combine flour, cinnamon, ginger, and salt.

Stir the flour mixture into the squash mixture.

Stir in cream, milk, and maple syrup.

In another bowl, beat egg whites with cream of tartar until soft peaks form.

Gradually add granulated sugar, one tablespoon at a time, beating continuously until stiff peaks form.

Gently fold the egg whites into the squash mixture thoroughly.

Pour the mixture into a well-buttered and sugared 2-quart souffle dish.

Place the dish in a baking pan.

Pour enough boiling water into the pan to reach 1 inch up the sides of the dish.

Bake souffle for 55 minutes, or until puffed and firm.

Sprinkle powdered sugar on top.

Let cool for 10 minutes before serving.