GF Southern Mac and Cheese

My kids love macaroni and cheese, what kids don't? Sometimes it's a nice meal for dinner, and although Annie's does make a gluten-free boxed option, it's not exactly what I'm craving for a real meal. In conseqeunce, I've tested a lot of recipes and come up with an amalgamation that I prefer. I found a recipe a few months ago for a more custardy base, that was indicated as a southern version of the classic. There are such great brown rice pastas out there that it's easy to swap them out for wheat pastas. This version was a winner at our house, so I thought I'd share it. I didn't measure everything out, so some of the measurements are approximations, but you get the idea. I feel that a lot of the fun of such comfort food casseroles is that you can work to make it your own.

8-10 oz brown rice pasta (elbow macaroni is most traditional, but I used small shells, Tinkyada makes great inexpensive versions of both)
1 Tbsp butter, melted
2 slices gluten free sandwich bread, torn
1 Tbsp butter (for frying pan)
1/4 cup diced sweet onion
1 3/4 cups shredded sharp cheddar (I used natural sharp cheddar, so it was white, but you really need to use sharp cheddar or the sauce is too mild and just not right, believe me, I've tried)
1/4 cup shredded parmesan cheese
2 eggs
1 cup half and half
1 clove garlic
salt and white pepper
1/4 tsp nutmeg (or to taste)
1/2 tsp thyme

Boil a large pot of salted water for cooking the pasta. Follow package directions, except to cook about three minutes shy of the suggested time, this will allow it to remain al dente, and not mush too much in the baking process. Preheat oven to 350 degrees.
Saute the onion in a small frying pan with some butter, until it's translucent. Remove to a large mixing bowl. Into the bowl add 1 1/4 cups sharp cheddar and the parmesan, half and half, beaten eggs, the pressed garlic clove and spices. Mix well. Once your pasta is done cooking, drain and add to the mixture in the large bowl. Mix to fully coat the pasta with the cheese mixture.
Pour pasta and cheese mixture into a 1 1/2 to 2 quart casserole dish. Top with the remaining 1/2 cup of cheese. In a food processor, pulse bread and the melted butter, until coarse crumbs form. Sprinkle the bread crumbs on top of the cheese layer. Bake in the oven for about 25-30 minutes, until the crumbs are golden and the cheese below is bubbly. Remove from oven and let sit for about 5 minutes before eating. Enjoy!