- In a bowl, add the yeast to the water and milk.
- In a stand mixer fitted with the dough hook, combine the flour, sugar and salt. Add the yeast mixture, egg yolk and melted butter. Knead the dough for 3 minutes or until smooth and elastic. Form into a ball. Place in a clean bowl and cover with plastic wrap. Let rise in a warm, humid spot for 1 hour or until doubled in volume.
- Meanwhile, place the butter cubes side by side in a 7-inch (18 cm) square sealable plastic bag. Do not close the bag. With a rolling pin, tap the butter to soften. Roll the butter layer out until it is the size of the bag and inch (1 cm) thick. Seal the bag. Lay out flat in the refrigerator until step 6.
- On a lightly floured surface, fold the risen dough over itself three times. Place in an 11-inch (27 cm) square sealable plastic bag. Do not close the bag. With a rolling pin, roll out the dough until it is the size of the bag. Seal the bag. Lay out flat in the refrigerator for 30 minutes.
- Remove the dough from the bag and place on a lightly floured surface.
- Remove the butter layer from the bag and place on an angle in the centre of the dough so it forms a diamond against the square of dough. Fold the four corners of the dough towards the centre over the butter layer, like an envelope, making sure to completely cover the butter. Seal the seams so the butter doesn’t escape during the folding process.
- Roll the dough out to a 22 x 9-inch (56 x 23 cm) rectangle. Cut the sides slightly to straighten them out. With a pastry brush, remove any excess flour. Fold both sides of the dough in towards the centre, and then fold in half to form a 9 x 4 1/2-inch (23 x 11.5 cm) rectangle. Cover with plastic wrap and refrigerate for 30 minutes. Repeat this step a second time. You can freeze the dough at this point, if desired.
- On a lightly floured surface, roll the dough to get a 22 x 9-inch (56 x 23 cm) rectangle. Cut the sides slightly to straighten them out. With a pastry brush, remove any excess flour. Cut the dough to get 4 equal rectangles of 9 x 5 1/2 inches (23 x 14 cm) each. Cut each rectangle into 2 long triangles.
- Make a 1-inch (2.5 cm) perpendicular incision in the centre of the short side of each triangle, starting at the edge. Starting from this side, using the palm of your hand, roll each triangle up tightly to get as many layers as possible (for the crispiest result). Place the croissants on a baking sheet lined with a silicone mat or parchment paper, spacing them out evenly. Place the baking sheet in a warm, humid spot, uncovered, for 1 hour 15 minutes, or until the croissants have doubled in volume (see note).
- With the rack in the middle position, preheat the oven to 350°F (180°C).
- In a small bowl, combine all the ingredients with a fork. With a pastry brush, gently brush the croissants with the egg wash, covering them completely.
- Bake for 25 to 30 minutes or until the croissants are golden. Let cool on a wire rack.
A great place to let your dough rise is in the oven, with the light on and a cup of very hot water placed directly on the rack. The ideal temperature for letting croissant dough rise is 81°F (27°C). Any hotter and the butter will seep out.