Preheat the oven to 375ºF. Spray a muffin tin with nonstick spray.

Cook the sausage in a skillet over medium heat, crumbling it with a wooden spoon until fully cooked. Add the butter. Once melted, stir in the garlic, onion, and bell pepper. Cook until the vegetables soften, about 5–6 minutes.

Prepare the egg mixture: While the sausage and vegetables are cooking, add the eggs, milk, salt, pepper, and garlic powder to a medium-sized bowl. Whisk until well combined. Fold in ½ cup of shredded Cheddar cheese.

Assemble the muffins: Using a tablespoon, divide the sausage mixture evenly among the muffin cups. Pour the egg mixture over each, trying to distribute the cheese evenly. Sprinkle the remaining ½ cup of Cheddar cheese on top of each muffin.

Bake for 15–18 minutes, or until puffed, golden brown, and set in the center. A toothpick inserted should come out clean.

Cool and serve: Let the muffins cool slightly, then run a knife around the edges to loosen before removing from the pan. Serve warm or at room temperature.