Finely slice the leeks, onion and mushrooms. Finely chop the garlic clove.

In your cast iron pan (or a nonstick pan that may go into the oven), sautée your veggies using a little olive oil. Start with the onion, then add the leek, and finish with the mushrooms. Season with salt and pepper. Add the garlic to aromatize.

Separately, in a bowl, mix the eggs, heavy cream or milk, and cheddar. You don’t need to whisk a lot, just mix the lot so that it becomes more or less homogeneous and incorporate into the pan.

With the help of a silicone spatula mix everything so that the egg and the veggies are well incorporated. If you want to add additional cheese on top, this would be the time to do so.

Leave your pan on the stovetop until the edges start to dry out. When said edges start to separate themselves slightly from the skillet, take it into the oven for about 9 minutes or as long as it takes for the eggs to become fluffy and look cooked all the way through.

Take out of the oven, let the frittata cool down and decorate with the herbs roughly chopped.