• Let the sour cream come to room temperature while you prepare the meat. This will prevent it from curdling when baked as it won't be going from cold to hot right away.
• Preheat oven to 350 degrees.
• Add the ground beef and diced onions to a large pan and cook and crumble over medium heat until the meat is cooked through.
• Drain excess grease.
• Add ¾ cup water and taco seasoning. Bring to a boil. Reduce the heat and simmer for 5 minutes, stirring occasionally. Remove from heat. Let it cool for 8-10 minutes.
• Spread the refried beans in an even layer in a lightly greased 9 x 13-inch casserole dish.
• Spread the sour cream over the refried beans, followed by the slightly cooled beef, then the cheese.
• If you’re preparing this head of time, let it cool and cover and refrigerate until ready to bake.

Baking:

• If baking right away: Bake, uncovered, for 15 minutes, or until the cheese is hot and melted.
• If baking after the casserole has been refrigerated: Bake, covered, for 25 minutes. Remove the cover and bake for an additional 5 minutes.

Add the toppings:

• Top the casserole with black olives and crunchy toppings. (Add additional cheese if you like as well.)
• Bake uncovered for 8 minutes.
• Garnish with green onions, diced tomatoes, and/or shredded lettuce and serve!