Impossibly Easy Cheesburger Pie

Impossibly Easy Cheesburger Pie
1 lb lean (at least 80%) ground beef
1 large onion, chopped (1 cup)
1/2 teaspoon salt
1 cup shredded Cheddar cheese (4 oz)
1/2 cup Original Bisquick® mix
1 cup milk
2 eggs

1.
Heat oven to 400°F. Spray 9-inch glass pie plate with cooking spray.
2.
In 10-inch skillet, cook beef and onion over medium heat 8 to 10 minutes, stirring occasionally, until beef is brown; drain. Stir in salt. Spread in pie plate. Sprinkle with cheese.
3.
In small bowl, stir remaining ingredients with fork or wire whisk until blended. Pour into pie plate.
4.
Bake about 25 minutes or until knife inserted in center comes out clean.
High Altitude (3500-6500 ft): Bake 30 to 35 minutes.