2Dice a large russet potato into small, bite-sized pieces.
3Throw the diced potatoes into a hot oiled pan, add salt and pepper, and cook with a lid, stirring occasionally, until soft.
4Remove the potatoes and drop a pound of ground beef into the same pan.
5Break up the ground beef and add half a diced white onion.
6Cook until the meat is browned and the onions are soft.
7Season with salt, pepper, about half a teaspoon of garlic powder, half a teaspoon of onion powder, and two teaspoons of yellow mustard.
8Stir everything together and cook for a minute or so.
9Mix the cooked ground beef and onions with the potatoes in the baking dish.
10Top with a handful of freshly shredded cheddar cheese.
11Cover with foil and put in the oven at 350°F for about 15 minutes.
12While the casserole bakes, prepare the Big Mac sauce: combine half a cup of mayonnaise, two tablespoons of sweet relish, a teaspoon of yellow mustard, half a teaspoon of paprika, half a teaspoon of onion powder, half a teaspoon of garlic powder, and a teaspoon of white vinegar in a bowl.
13Whisk until beautifully combined.
14Once the timer goes off, remove the casserole from the oven and rip the foil off.
15Cover the casserole with the homemade Big Mac sauce.
16Top with fresh shredded lettuce, one diced tomato, some diced white onions, and chopped pickles.
17Cut a piece out with a spatula and serve on a plate.