3 pounds christophene, peeled, seeded and cut into cubes (can substitute chayote or any summer squash)
4 tablespoons butter
4 tablespoons flour
1 1/4 cups milk
1/2 cup grated Monterey jack or Cheddar cheese, plus 1 cup, for topping
1 onion, finely chopped
2 cloves garlic, finely chopped
1 teaspoon salt
1 tablespoon chopped celery
2 teaspoons prepared mustard
2 tablespoons sugar
Fill a large pot with water and add a little salt. Bring the water to a boil, then add the cubed squash and cook until tender, about 10 minutes. Drain the cooked squash and set aside in a large, well-greased baking dish.
Preheat oven to 350 degrees F.
In a large saucepan over low heat, melt the butter. Slowly whisk in the flour and cook for 1 to 2 minutes, until the mixture is creamy and thick. Slowly stir in the milk and mix until smooth, about 1 minute. Add the 1/2 cup of grated cheese and stir until melted and well-mixed, about 1 minute. Add the onion, garlic, salt, celery, mustard and sugar to the sauce and mix well. Remove the sauce from heat and pour over the christophene in the baking dish. Stir everything together, then top with the remainig 1 cup grated cheese.
Place the mixture in the oven and bake until golden brown, about 20 to 30 minutes. Serve warm.