Preheat oven to 425°F (220°C).

Prepare ingredients: slice 8 ounces mushrooms, thinly slice 1 shallot, mince 1 clove garlic, destem and roughly chop 1 cup packed kale leaves, and have 2 tablespoons unsalted butter and 1/4 cup grated Parmesan ready.

Heat an oven-safe 10–12 inch skillet over medium heat and add the 2 tablespoons butter. When the butter is melted and foaming, add the sliced mushrooms, sliced shallot, and 1/2 teaspoon dried thyme. Cook, stirring occasionally, until the mushrooms are golden and most of their liquid has evaporated, about 8 minutes.

Add the minced garlic and the chopped kale to the skillet. Cook, stirring, until the kale is wilted, about 2 minutes. Remove the skillet from the heat.

In a bowl, whisk together 8 large eggs, 1/4 cup milk, 1/2 teaspoon sea salt, and 1/4 teaspoon ground black pepper until combined and slightly frothy.

Pour the egg mixture evenly over the cooked vegetables in the skillet. Return the skillet to the stovetop over medium-low heat and cook without stirring until the edges begin to set, about 2–3 minutes.

Evenly sprinkle the 1/4 cup grated Parmesan over the eggs, then transfer the skillet to the preheated oven. Bake until the center is set and the edges are golden, 10–12 minutes. A knife inserted near the center should come out clean or with very slight moisture.

Remove the skillet from the oven and let the frittata rest for 5 minutes.

Sprinkle chopped parsley over the top for garnish, slice, and serve.