In a saucepan, melt 2 Tbsp butter, whisk in flour and then stir in milk. Cook for a minute until it thickens. Remove from heat.
In a bowl, combine potatoes, above flour mixture, onions, sour cream, 2 Tbsp melted butter, garlic, salt, pepper, cheese and green onions.
Stir to combine.
Place potatoes in a 8 x 5 inch baking dish
Combine 2 Tbsp melted butter and bread crumbs. Sprinkle on top of potatoes.
Bake at 350 degree F for 40-45 minutes or until heated through, bubbly and golden brown around the edges.
Video
Notes
You can bake the hash browns frozen, your bake time will just vary slightly and take a bit longer.If you prefer a shredded potato rather than a diced potato, that will work too.