1Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In 10-inch skillet, cook sausage and onion over medium-high heat 5 minutes, stirring occasionally. Stir in potatoes. Cook 5 to 7 minutes, stirring occasionally, until sausage is no longer pink and potatoes are lightly browned. Drain mixture on paper towels; spoon into baking dish.
2In medium bowl, stir eggs, milk, Bisquick mix, salt and pepper with fork or whisk until blended. Stir in cheese. Pour over sausage mixture and stir well. Cover with nonstick foil; refrigerate 8 to12 hours.
3Heat oven to 350°F. Bake casserole covered 45 minutes. Uncover; bake 10 to 15 minutes longer or until knife inserted in center comes out clean. Let stand 5 minutes before serving. Serve with picante sauce and sour cream.