Preheat oven to 375°F (191°C).

In a medium bowl whisk together the eggs, milk, salt, and pepper. Whisk in about 3/4 cup of the cheese, reserving the rest for topping. Set aside.

Heat olive oil in a 2-inch-deep, 10- to 12-inch-diameter oven-safe skillet over medium heat. Add the garlic and cook, stirring, for about 30–60 seconds (don’t let it brown).

Fold the spinach, tomatoes, artichoke hearts, and prosciutto into the egg-and-cheese mixture.

Pour the egg-and-cheese mixture into the pan with the cooked garlic and cook for 5 minutes, without stirring, until bubbling/starting to set around the edges. Sprinkle the remaining 1/4 cup cheese on top.

Carefully transfer the skillet to the center rack of the oven, and bake for 20–25 minutes, until the frittata is puffy and the center no longer wobbles/looks wet.

Transfer the skillet to a wire rack, and let it cool for at least 10 minutes before slicing and serving. Frittata will continue to set as it cools.