This is my favorite way of making macaroni and cheese; it's a great way to slip in extra protein and vegetables without the kids really noticing.
2 C cooked chicken, cut into 1 inch cubes
2 C steamed broccoli, cut into bite-sized pieces
3 T butter
3-4 T white rice flour (superfine)
2 C heavy cream
2 C chicken broth
2 tsp salt, plus more for water
1/4 tsp ground dry mustard
1/4 tsp freshly ground black pepper
3 T onion flakes
1/2 tsp garlic powder
2 1/2 C grated sharp white cheddar cheese
1 1/2 C grated medium cheddar
1 1/2 C grated monterey jack
1 1/2 C grated Jarlsberg
1 C grated Parmesan
1 pound gluten free elbow macaroni
Preheat oven to 350°F. Lightly oil a 3-quart casserole dish.
Melt the butter in a saucepan over medium heat. When the butter bubbles, add the rice flour. Cook, stirring (best to use a wire whisk), for about 1 minute. While whisking, slowly pour in the cream a little at a time to keep mixture smooth, until the mixture bubbles and becomes thick. Continue cooking, and add the chicken broth a little at time while whisking constantly, until the mixture has the thickness and consistency of paint. You don't want it to be too thick, because it will thicken when you add the cheese. Note: you may not need to add all of the broth to reach the right consistency.
Remove the pan from the heat. Stir in salt, dry mustard, black pepper, garlic powder, onion flakes, all of the Parmesan and MOST of the other cheeses (reserve a little of the grated cheddars and Jarlsberg to sprinkle on top); set the cheese sauce aside.
Bring a large pot of salted water to a boil. Cook the macaroni until al dente (i.e., until the outside of the pasta is cooked and the inside is slightly underdone), about 7-8 minutes for most gluten free pastas, but it varies. Drain the macaroni in a colander and return to the empty pot. Add the chicken, broccoli and cheese sauce to the macaroni; mix well but gently.
Pour the mixture into the prepared casserole dish. Sprinkle the remaining grated cheddar cheese over the top. Bake until top is starting to turn golden brown in spots, about 20 - 25 minutes.