Cheddar Cabbage Casserole - a favorite supper on a cold and wintery night

I like to serve this with a congealed cranberry salad for a perfect comfort food supper, especially on a wintery night. It serves a bunch, kids like it and there's no rice or noodles for those who are watching the carbs. People who protest to eatting cabbage will ask for seconds!
8 cups thinly sliced green cabbage
2 large carrots, peeled and finely chopped
1 small can mushrooms, chopped
1 large yellow onion, finely chopped
8 tablespoons butter, divided
5 tablespoons all-purpose flour
1/8 teaspoon garlic powder
1 tablespoon brown sugar
2-1/4 cups milk
2 cups shredded, cheddar cheese
1/2 cup sour cream
1 can cream of celery soup
1 pound sausage, cooked, crumbled, and drained
3/4 cup seasoned bread crumbs, home-made are best
Salt and fresh cracked pepper to taste
Add the cabbage and carrots to boiling salted water and cook only 5 minutes, until crisp-tender. Meanwhile, in a saucepan, sauté the onion in 6 tablespoons of butter until tender. Stir in flour, salt and pepper; cook until bubbly. Gradually add milk and sour cream; cook and stir until thickened. Drain cabbage and carrots, add mushrooms, brown sugar, salt and pepper; stir; add the sausage and the sauce and mix well. Add half the cheese and mix. Put into greased casserole dish; sprinkle with remainder of cheese. Adjust milk for desired consistency.
In a small skillet, melt remaining butter. Add crumbs; cook and stir until lightly browned. Sprinkle over casserole. Bake, uncovered, at 350 degrees for 40-45 minutes or until the cabbage is tender and top is golden brown.