Preheat the oven to 425˚F (220˚C, or gas mark 7).

Heat the olive oil in an 8-inch (20 cm) cast-iron or other oven-safe skillet over medium-low heat.

In a large bowl, whisk together the eggs, milk, salt, and pepper.

Pour into the skillet and cook for 5 to 6 minutes, until the bottom is set.

Sprinkle the cheese on top.

Transfer to the oven and bake for another 12 to 16 minutes, until the frittata has puffed up, doesn’t jiggle, and is beginning to brown.

Remove and let cool slightly before slicing.