Place 1 teaspoon butter in a small microwave-safe bowl and microwave until just melted, about 10–15 seconds; brush the melted butter evenly over the inside of the bowl.
Crack 4 large eggs into the bowl, add 2 tablespoons milk or heavy cream, and season with a generous pinch of salt and a pinch of black pepper. Whisk until combined.
Microwave the eggs uncovered for 30 seconds. Remove and gently stir with a fork to break up the curds.
If using, add about 1/4 cup shredded cheddar cheese and stir gently into the eggs.
Return the bowl to the microwave and cook an additional 45 seconds or until the eggs are fluffy and almost set. Let stand briefly, then serve immediately.