1/3 cup gf macaroni noodles, uncooked 2 Tablespoons unsalted butter 2 Tablespoons gf flour 1/2 teaspoons salt 1/2 teaspoon dry mustard 1/8 teaspoon freshly ground black pepper 1 cup milk 1-1/2 cup cheddar cheese, grated 4 eggs, separated
Cook macaroni noodles according to package directions. Drain noodles and chop coarsely.
Preheat oven to 350°F.
Melt butter in a small saucepan. Add gf flour, salt, pepper and dry mustard; mix until blended. Gradually whisk in milk. Cook over medium heat, stirring constantly, until thickened and sauce starts to bubble. Remove from heat and stir in cheese until cheese is thoroughly melted. Stir in macaroni and let cool for 1 minute.
Beat egg yolks until thick. Fold into macaroni mixture. Beat egg whites until stiff. Slowly pour egg whites on top of macaroni mixture, folding lightly.
Butter a 1-1/2 quart casserole and lightly dust with gf flour. Pour macaroni mixture into casserole. Put casserole dish into a baking pan, fill pan with hot water (about 1 inch up the sides of the casserole). Bake for 1 hour, or until somewhat dry when touched lightly with your finger.