A delightful frittata featuring the classic Caprese flavors of tomatoes, basil, and cheese combined with eggs for a delicious breakfast or brunch dish.
Preheat the oven to 350°F (180°C).
In a small bowl, lightly beat the eggs with the milk until the yolks mix well with the whites, being careful not to overmix. Add the basil, salt, and pepper and stir until well combined.
Heat the olive oil in a 10-inch (25 cm) ovenproof skillet over medium-high heat. Add the onion and sauté until softened, 3 to 4 minutes. Add the garlic and stir for 30 seconds, until fragrant.
Spread the onions and garlic evenly over the bottom of the skillet. Pour the egg mixture on top, then reduce the heat to medium. Sprinkle the eggs with the tomatoes, then top with the sliced cheese. Cook until the edges start to set and pull away gently from the pan, about 5 minutes.
Transfer the skillet to the oven and bake for 15 to 17 minutes, until the frittata pulls slightly away from the edges and is set throughout.
Sprinkle the frittata with fleur de sel and fresh basil. Slice into wedges and serve warm or at room temperature.