Cut the butter in four 1-Tablespoon pieces and place in the bowl of an electric stand mixer fitted with the dough hook attachment. Add the flour, sugar, salt, and yeast. Turn the mixer on low-medium speed to gently combine the ingredients for 1 minute. Slowly pour in the milk.

Knead the dough: Keep the dough in the mixer and beat for an additional 5 full minutes, or knead by hand on a lightly floured surface for 5 full minutes.

Remove dough from the bowl and work it into a ball. Place the dough on a lightly floured silicone baking mat or baking sheet. Gently flatten the dough and cover with plastic wrap. Place in the refrigerator for 30 minutes.

Remove the dough from the refrigerator and roll it into a 14x10-inch rectangle. Cover the rolled out dough and chill for 4 hours or overnight.

In a large bowl, beat the butter and flour together until smooth. Transfer to a baking sheet and smooth out into a 7x10-inch rectangle. Chill for 30 minutes.

Remove both the dough and butter layers from the refrigerator. Place the butter layer in the center of the dough and fold each end of the dough over it. Roll the dough into a 10x20-inch rectangle and fold lengthwise into thirds. This is the 1st turn.

Refrigerate for 30 minutes before the 2nd turn. Roll the dough out again into a 10x20-inch rectangle and fold lengthwise into thirds. Refrigerate for 30 minutes before the 3rd turn.

Roll the dough out once again into a 10x20-inch rectangle and fold lengthwise into thirds. Refrigerate for 4 hours or overnight.

Remove the dough from the refrigerator and roll it out into an 8x20-inch rectangle. Cut the dough into triangles and shape each triangle into a crescent shape.

Loosely cover the shaped croissants and allow to rest at room temperature for 1 hour, then refrigerate for 1 hour.

Preheat oven to 400°F (204°C). Whisk the egg wash ingredients together and brush each croissant lightly.

Bake until golden brown, about 20 minutes. Rotate the pans halfway through baking.