Place the flour, sugar, yeast, and salt in the bowl of a stand mixer. Whisk together.

Using the hook attachment, with the mixer at low speed, stream in the water. Combine the dough for 2 minutes at low speed, then increase to medium for 5 minutes.

Dust a silpat mat or parchment paper with flour and stretch the dough into a rectangular shape. Move it to a baking sheet and cover with plastic wrap. Allow to rest in the refrigerator for at least 4 hours or overnight.

Fold a large sheet or two small sheets of parchment paper into an 8×10" rectangle. Slice the butter in half lengthwise and place it in the folded parchment paper. Roll the butter out into the shape of the parchment paper.

Refrigerate the butter for 5-10 minutes until malleable but not greasy.

Remove the dough from the fridge, roll it out to 16×10" on a lightly floured surface. Place the butter in the center of the dough.

Fold the top and bottom 1/3 of the dough over the butter and seal the edges. Turn the dough 90 degrees and roll it back out to 16×10".

Fold the dough into thirds like a letter. Cover with plastic wrap and refrigerate for 10 minutes. Repeat this folding process 2 more times. After the last fold, cover and refrigerate for at least 2 hours (preferably 4 or more).

Remove the dough from the fridge and let it rest at room temperature for about 15 minutes. Roll out to about 24×12" and trim edges into a rectangle.

Slice the dough into long triangles. Flatten the tips of each triangle and roll them from the wide end to the tip.

Place 4-6 croissants on a lined baking sheet and cover loosely with plastic wrap. Allow to proof at room temperature for about 2 hours.

Preheat the oven to 400F (204C). Beat the egg and egg wash the croissants.

Bake the croissants for 15-18 minutes until golden brown. Cool on the pan for 10-15 minutes before transferring to a cooling rack.