In a large skillet, brown the ground beef. Drain off any excess fat.
In a medium saucepan, combine tomato sauce, ketchup, brown sugar, and mustard. Bring to a boil over medium heat. Add cooked beef to sauce mixture.
Spoon the hot meat mixture into an ungreased 13×9×2-inch baking pan.
In a medium mixing bowl, whisk together the Bisquick, milk, and eggs until blended.
Carefully pour the Bisquick mixture evenly over the beef layer.
Bake for 20-25 minutes or until the top is light golden brown.
Serve warm!
Notes
Pour the Bisquick mixture carefully: Do your best to pour the Bisquick mixture slowly over the beef mixture so it stays on top and doesn’t sink to the bottom. Spreading it evenly helps the topping bake consistently.
Let it rest before serving: Allowing the bake to cool for a few minutes after removing it from the oven helps it set and makes slicing and serving much easier.
Drain the beef well: Be sure to drain off excess grease after browning the ground beef to prevent the casserole from becoming greasy or soggy.
Simmer the sauce briefly: Letting the sloppy joe sauce simmer for a few minutes helps thicken it slightly and deepen the flavor before baking.
Use a deep baking dish: A standard 9×13-inch dish works best and helps prevent bubbling over while the casserole bakes.
Don’t overmix the Bisquick batter: Stir just until combined—overmixing can lead to a dense or tough topping.
Check for doneness at 20 minutes: Oven temperatures can vary, so start checking around the 20-minute mark to avoid overbaking.
Golden, not dark: The topping should be lightly golden brown on top; if it starts browning too quickly, loosely tent with foil.