In a mixing bowl, combine flour, sugar, salt, and yeast.

Add cold unsalted butter and mix until crumbly.

Gradually mix in the milk until the dough comes together.

Knead the dough for about 10 minutes, then shape into a ball and cover it.

Refrigerate the dough for at least 2 hours.

Roll out the dough, then place the cold unsalted butter in the center and fold the dough over it.

Roll the dough out again and fold into thirds to create layers.

Repeat the rolling and folding process two more times.

Cut the dough into triangles and roll each triangle from the base to the tip.

Place rolled croissants on a baking sheet and let them rise for 1 hour.

Preheat the oven to 400°F (200°C).

Brush croissants with a mixture of egg yolk and milk or water before baking.

Bake for 15-20 minutes until golden brown.