Easy Chicken and Noodles

Ingredients: – 2 tablespoons butter – 1 onion, diced – 1 tablespoon minced garlic – 2 cups chicken broth – 1 can cream of mushroom soup – 3 cups egg noodles, uncooked – 2 cups cooked and shredded chicken – 1/2 cup half and half – Boxed mashed potatoes, plus ingredients on box – Salt and pepper, to taste