Combine frozen hash browns, cheese, and onion in a large bowl.
Combine the milk, beef stock, half the melted butter, the garlic powder, salt, and black pepper in another bowl. Mix until well blended, then pour the mixture over the hash browns and mix well.
Heat the remaining butter in a large, ovenproof skillet (no plastic handle) over high heat.
When the skillet is hot, spoon in the hash brown mixture. Cook the hash browns, stirring occasionally, until hot and all of the cheese has melted (about 7 minutes). Put the skillet into the oven and bake for 45 to 60 minutes or until the surface of the hash browns is dark brown.
Notes
This recipe comes from one of my favorite cookbooks, "Top Secret Restaurant Recipes" by Todd Wilbur.
Since there are just two of us at my house, I usually make this and bake ½ of the batch, freezing the other half of the other half. When I need a larger batch, I double the batch. I freeze before baking and freeze in the small Pyrex casserole dish that I'll later cook it in. I'm sure that this would also freeze well in a heavy duty freezer bag.
Recipe by DealsFromMsDo.com at https://dealsfrommsdo.com/cracker-barrel-hashbrown-casserole/