Preheat the oven: Set it to 350°F (175°C). Grease a 12-cup muffin tin well with olive oil or butter.
You can also use silicone liners for easy release.
Prep the mix-ins: Dice the ham into small pieces. Chop green onions and veggies if using. Keep everything in small bits so they distribute evenly.
Whisk the eggs: In a large bowl, whisk eggs, heavy cream, Dijon, garlic powder, onion powder, salt, and pepper until smooth and slightly frothy.
Add the good stuff: Stir in ham, shredded cheddar, Parmesan, and any veggies or green onions.
Mix to combine, but don’t overwork it.
Fill the muffin cups: Divide the mixture evenly among the 12 cups. Each should be about three-quarters full. Give the pan a gentle tap on the counter to settle the mixture.
Bake: Place on the center rack and bake 18–22 minutes, until the tops are set and lightly golden and a toothpick comes out clean.
They will puff up and then settle slightly as they cool.
Cool and release: Let them cool in the pan for 5 minutes. Run a thin knife around the edges to loosen, then lift out and set on a rack.
Serve: Enjoy warm as-is, or top with a little hot sauce, avocado, or a dollop of sour cream.