Gluten-Free Chicken Broccoli Cheese Casserole

We have a missionary in our area who has Celiac's and can't have gluten.  We have fed them twice now and both times, I had to rack my brain for ideas.  Luckily I found this lady's blog. glutenfreemommy.com.  We really liked this casserole - even better than when we use cream of mushroom soup. But it doesn't have to be gluten-free if ya don't want it to be.

1 lb cooked chicken, shredded
1 lb fresh broccoli, chopped
2 tablespoons butter
2 tablespoons of rice or soy flour (can use all purpose here if ya don't need it to be gluten-free)
1/2 teaspoon salt
1/4 teaspoon pepper
1/2 teaspoon dried mustard
1 1/2 cups milk
squeeze of lemon juice
1 tablespoon mayonnaise
1 1/2 cups shredded cheddar cheese
1/2 cup gluten-free breadcrumbs (I found some at Sprouts, but you can use regular breadcrumbs here if you don't care about gluten.)
slivered almonds for topping

Melt the butter in a medium saucepan.  Add the flour, salt, pepper, mustard, and cook 2-3 minutes until bubbly and foamy. Slowly whisk in the milk and stir until thickened.  Stir in the shredded cheese.  Place the rice, chicken and broccoli in casserole dish. Pour white sauce on top. Top with breadcrumbs and almonds. Bake uncovered at 350 for 30 minutes.