Cheesy Potatoes

This is a recipe that my mom gave me and I've made it many times when company is coming or we are having a party.  It's the dish that people most comment on and I always run out.  I like it because I can make it early in the day in advance and then slide it into the oven an hour and a half before serving it.  

4 pounds frozen hash browns
1 large yellow onion, chopped (This is my addition to the recipe)
1 pint half and half
1 1/2 cups butter (3 sticks)
1 pound Velveeta

Line a large baking pan with heavy-duty foil.  Spray foil with non-stick cooking spray.  Pour hash browns and chopped onions into the pan.  Break up any clumps and mix the onions with the hash browns.

Melt half and half, butter, and Velveeta together, in a pan, over low heat.  Stir frequently so it doesn't burn on the bottom.  Pour over hash brown mixture in pan.  Mix together.  Refrigerate for at least one hour.

Bake uncovered at 350 degrees for 1 1/2 hours until browned.