Preheat the oven to 350°F. Grease the bottoms, sides, and upper edges of all 12 cups in a standard muffin pan.

Cook the breakfast sausage in a skillet over medium heat, breaking it into small crumbles, until browned and cooked through with no pink remaining. Drain the excess fat and let the sausage cool for a few minutes.

Beat the eggs in a large bowl. Add the Bisquick baking mix and shredded cheddar, then stir just until the dry mix is moistened.

Stir the cooked, drained sausage into the batter until the crumbles are evenly distributed. The mixture will be thick and chunky; do not add milk.

Divide the batter evenly among the 12 prepared muffin cups, filling each about three-quarters full.

Bake for 18 to 20 minutes, or until the tops and centers are set and the edges are lightly golden. The centers should not wobble or look wet. If needed, bake for another minute or two and check again.

Let the muffins cool in the pan for a few minutes. Gently loosen the edges with a thin spatula, then lift the muffins onto a rack or serving plate.

Serve warm. The inside should be cooked through, tender, and full of sausage and cheddar. A modest rise and a substantial, egg-rich crumb are normal for these muffins.