Get your oven ready for baking by preheating it to a warm 400°F (204°C).
In a large skillet, cook your ground Italian sausage over medium-high heat. Break it apart with a wooden spoon as it cooks until it's nicely browned, which usually takes about 8-10 minutes.
While the sausage is cooking, prepare a 12-cup muffin tin. You can line each cup with parchment paper or silicone liners, or simply give them a quick spray with cooking spray to prevent sticking.
Once the sausage is browned, divide it evenly among the prepared muffin cups – about 3 tablespoons for each. Then, sprinkle a tablespoon of shredded cheese on top of the sausage in every cup.
In a separate large bowl, whisk together the eggs, heavy cream (or milk), sea salt, and black pepper until everything is well combined and slightly foamy.
Carefully pour the egg mixture into each muffin cup, filling them over the sausage and cheese. Allow it to settle for a few seconds, then top off with a bit more if there's room.
Bake your sausage egg muffins in the preheated oven for 15-20 minutes, or until the eggs are completely set and look lightly golden. Let them cool slightly before enjoying!