01 -
Preheat oven to 375°F (190°C). Place the unbaked 9-inch deep-dish pie crust in a pie dish and set aside.
02 -
In a large skillet over medium heat, cook the ground beef and chopped onion until the beef is well browned and onions are tender, about 7 to 9 minutes. Drain any excess fat from the skillet.
03 -
Add minced garlic, ketchup, mustard, salt, and black pepper to the skillet. Stir to combine thoroughly and cook for 1 to 2 minutes. Remove skillet from heat.
04 -
Transfer the beef mixture into the prepared pie crust, spreading evenly. Sprinkle shredded cheddar and mozzarella cheeses evenly over the beef layer.
05 -
In a medium bowl, whisk together eggs, milk, and flour until smooth and homogeneous. Pour this mixture evenly over the cheese and beef layers in the pie.
06 -
Place pie in preheated oven and bake for 25 to 30 minutes, or until the top is golden and the center is set. Remove from oven and let rest for 5 to 10 minutes before slicing.
07 -
Serve warm. For added flavor, garnish with sliced pickles or chopped tomatoes, or accompany with a fresh green salad if desired.