Preheat oven to 350 degrees and cook pasta according to package instructions.
While pasta cooks heat a large skillet. Melt butter and add carrots and onions. Saute for a few minutes. Add garlic and mushrooms and cook until mushrooms sweat a bit. Set veggie blend to the side.
In the same skillet begin sauce. Melt the butter and sprinkle with flour. Whisk with a fork to create a paste. This begins the roux.
Slowly add chicken broth and half and half. Whisk as you do to avoid lumps and fully incorporate. Heat at a simmer until sauce thickens.
Add seasonings and Parmesan. Turn off the heat and mix in sour cream. Taste and add additional seasoning if needed.
Now it’s time to combine everything! In a greased 9×9 baking pan or medium size cast iron add pasta, veggie blend, pea, drained meat, cheese, and sauce. Toss to coat.
In a small bowl melt topping butter and mix in bread crumbs. Sprinkle the buttered bread crumbs and Parmesan on top and bake for 30 minutes or until the casserole is bubbling and the topping is golden brown.