Step 1

Place 3 cups all-purpose flour and 1/2 teaspoon kosher salt in a large bowl and whisk to combine. Cut 1 1/2 sticks cold unsalted butter into small cubes and add to flour. Using your hands or a pastry cutter, mix the butter into the flour until no large butter chunks remain and the flour resembles sand.

Step 2

Add 1 large egg and lightly whisk to combine. Slowly mix in 1/2 cup whole or 2% milk a little bit at a time with your hands until the dough is soft and smooth. Divide the dough in half and form each piece into a ball.

Step 3

Dust a work surface lightly with all-purpose flour. Roll each ball out with a rolling pin until 1/4-inch thick. Cut out 5-inch wide rounds with a cutter, or trace a plate or other round object with a knife to cut. Transfer the rounds to a wax or parchment paper-lined plate or baking sheet, placing more paper between each layer.

Step 4

Gather the scraps into a ball, then re-roll and cut more rounds out until you have a total of 12 to 14 rounds. Refrigerate while you make the filling, at least 25 minutes.

Step 5

Dice 1/2 medium white onion (about 3/4 cup) and mince 1 garlic clove. Shred 6 ounces mozzarella cheese on the large holes of a box grater (about 1 1/2 cups). If needed, finely grate 1 ounce Parmesan cheese until you have 3 tablespoons.

Step 6

Heat 3 tablespoons olive oil in a 10-inch frying pan over medium heat until shimmering. Add the onion and garlic and sauté until the onion is softened, 3 to 5 minutes.

Step 7

Add 9 ounces baby spinach a few handfuls at a time, stirring between addition, until wilted, about 4 minutes. Reduce the heat to low. Add the mozzarella, Parmesan, 3 tablespoons cream cheese, mozzarella, 1/4 teaspoon kosher salt, and 1/4 teaspoon black pepper. Stir until the cheeses are melted and everything is combined, about 2 minutes.

Step 8

Remove from the pan from the heat. Taste and season with more kosher salt and black pepper as needed.

Step 9

Arrange a rack in the middle of the oven and heat the oven to 400°F. Line a rimmed baking sheet with parchment paper or aluminum foil. Whisk 1 large egg and a few drops of water in a small bowl with a fork until lightly beaten. Whisk 1 large egg yolk in a second small bowl until lightly beaten.

Step 10

To assemble the empanadas, place 2 tablespoons of the warm spinach filling in the center of a disc of dough. Brush the edges of the disc with the egg white wash. Fold the disc in half over the filling. Press the edges with your fingers to seal. Press a fork onto the edges about 1/2-inch in to further and decoratively seal. Place on the baking sheet.

Step 11

Repeat filling the remaining empanada discs, spacing them evenly apart on the baking sheet. (If you have filling leftover, save it and enjoy as a snack with chips.) Brush the empanadas with with egg yolk wash.

Step 12

Bake until the empanadas are golden-brown, 20 to 25 minutes. Let cool for 5 minutes on the baking sheet before serving.