Step 1

1 In a medium saucepan over medium heat, combine the spinach with a pinch of salt, cover and cook to warm through and release any liquid, 1 to 2 minutes

Step 2

2 Remove from the heat, drain

Step 3

3 In a 6- to 8-inch ovenproof nonstick or cast-iron skillet over medium-high heat, heat the olive oil and garlic cloves, stirring until the cloves turn a deep golden color, about 5 minutes

Step 4

4 Discard the garlic

Step 5

5 Add the spinach and a pinch of salt, and cook, stirring, so the spinach picks up all the garlicky oil, about 1 minute

Step 6

6 Transfer the spinach to a plate

Step 7

7 Wipe out the pan

Step 8

8 Position a rack 5 to 6 inches from the broiler and preheat

Step 9

9 In a medium bowl, whisk the eggs and milk

Step 10

10 Then, whisk in half the mozzarella, half of the Parmesan, a few generous pinches of salt and pepper, and a pinch or two of ground nutmeg, if using, until thoroughly incorporated

Step 11

11 Using a slotted spoon, drain the spinach and add it to the egg mixture

Step 12

12 Whisk again to combine

Step 13

13 Using the same pan over medium heat, melt the butter until it starts to foam but doesn’t start to brown

Step 14

14 Briefly re-whisk the egg mixture and pour it into the pan

Step 15

15 Give the batter a few stirs with a rubber spatula to make sure the spinach is evenly distributed

Step 16

16 Decrease the heat to low and let the frittata cook, shaking the pan occasionally, until only the surface remains runny, 6 to 8 minutes

Step 17

17 (The edges should be completely set, and the interior should be thickened and custardy

Step 18

18 )

Step 19

19 Dot the top of the frittata with the ricotta and sprinkle it with the remaining mozzarella and Parmesan

Step 20

20 Transfer the pan to the oven and broil for about 2 minutes, until the top sets and the cheese melts and forms a golden brown crown

Step 21

21 Transfer the frittata to a wire rack and let cool until warm or at room temperature

Step 22

22 Slice and serve with the tomato sauce poured over the top and, if desired, a sprinkling of fresh basil