Preheat oven to 400 degrees. Coat 9×13 inch casserole dish with cooking spray
Boil salted water in a large pot. Add green beans and cook for 6-7 minutes. Drain water. Set aside.
In a medium saucepan set over med-high heat, melt butter. Add minced garlic and stir continuously for 20 seconds so garlic doesn’t burn. Whisk in flour until smooth.
Add chicken broth to saucepan. Stir and cook for 2-3 minutes. Add heavy whipping cream or half and half. Stir and set heat to Low. Let simmer for 10-13 minutes until sauce thickens. Season with salt and black pepper.
Pour green beans into casserole dish and spread into an even layer. Pour sauce over the green beans. Top with French’s fried onions.
Bake in oven for 20-25 minutes. (Place loose foil over the top during the last 10 minutes of cooking to prevent onions from burning.)
Remove from oven. Let cool for a few minutes before serving.