Pioneer Woman Cheeseburger Pie

INGREDIENTS

1 large onion, chopped (1 cup)
1 pound ground beef
½ teaspoon salt
Ground black pepper, to taste
Garlic powder, to taste (optional)
1 cup grated Cheddar cheese
½ cup Original Bisquick mix (or all-purpose flour)
1 cup whole milk
2 large eggs

INSTRUCTIONS