Sour Cream Chicken Strata

2 Tbsp butter
1/2 lb. French bread cut into 3/4″ cubes
2 Tbsp olive oil
1 small onion thinly sliced
2 large boneless chicken breasts cut into 3/4″ cubes
1 can fat-free or healthy request cream of condensed celery soup (NOT
diluted)
2 eggs
3-4 Tbsp French onion soup mix (dry)
3/4 cup sour cream (regular; do NOT use low-fat or fat-free)
4 oz cheese (Monterey Jack or cheddar or whatever) grated (~1 cup)

In 12″-inch oven-proof skillet, melt butter until it foams. Add bread cubes
in one go and toast in skillet stirring occasionally. Remove bread cubes
from skillet. Add olive oil to skillet and heat until fragrant. Add sliced
onion and saute.