Preheat your oven to 400°F. In a large skillet over medium heat, combine the ground beef and chopped onion, cooking until the meat is fully browned and the onion is tender. Drain any excess grease and transfer the mixture into a greased 9-inch pie dish, spreading it evenly.

Evenly scatter the shredded cheddar cheese over the beef layer.

In a separate bowl, whisk together the milk, eggs, Bisquick, and onion soup mix until fully blended. Carefully pour this mixture over the contents in the pie plate.

Place the dish in the oven and bake for 25 minutes, or until the center is set and the top is golden. Allow the pie to cool slightly before slicing and serving.