In the bowl of a stand mixer, combine warm water and yeast. Let the yeast dissolve for 10 minutes. Add sugar, bread flour, salt, and 6 tablespoons of butter. Attach the bowl to the stand mixer and mix the dough with the dough hook until the butter is completely kneaded in and the dough forms a ball, pulling away cleanly from the sides of the bowl, about 3-4 minutes.

Transfer the dough to a work surface and shape it into a semi-smooth ball. Place the dough back in the mixer bowl, cover it, and let it rise in a warm spot until doubled in size, about 2 hours.

Transfer the dough to a lightly floured work surface and shape it into a rectangle. Fold the dough into thirds by lifting one end over the middle third, and then folding the other side onto the middle. Wrap the dough in plastic wrap and refrigerate until chilled, about 1 hour.

Cut the sticks of butter in half lengthwise and place them slightly apart on a piece of parchment paper. Fold the parchment paper over the butter and press it down. Roll out the butter to form a square about 8x8 inches. Refrigerate until slightly chilled and just barely flexible, about 10-15 minutes.

Roll out the dough into a rectangle slightly wider than the butter slab and just over twice as long. Place the butter on one half of the dough, leaving about a 1-inch margin from the edge. Fold the other half of the dough over the butter. Dust the work surface and dough with flour as needed.

Press down on the dough with a rolling pin to create ridges, then roll out the ridges. Repeat this process until the dough is about the same size rectangle as before folding it in half, dusting with flour as necessary.

Fold one-third of the dough over the middle third, then fold the other end over to form a small rectangle. Flatten it slightly with a rolling pin. Transfer the dough to a silicone-lined baking sheet, cover it with plastic wrap, and refrigerate until chilled, about 30 minutes.

Repeat the pressing and rolling technique until the dough is the size of the previous larger rectangle. Fold it into thirds again, starting from the short side. Press and roll it slightly, then transfer it back to the lined baking sheet, cover, and refrigerate for about 15 minutes.

Roll out the dough to a large rectangle, then fold it in half. Press and roll it out into a 1/2-inch thick rectangle, using as little flour as needed to prevent sticking.

Cut the dough in half lengthwise and dust one piece with flour. Roll it out into a rectangle about 1/4 to 1/8 inch thick. Using a pastry wheel or pizza cutter, cut the dough diagonally crosswise into 8 triangles. Starting from the bottom end of each triangle, roll it up toward the tip to form a croissant with the seam at the bottom. Seal the tip if necessary with a bit of water.

Repeat the process with the other half of the dough.

Place the shaped croissants on baking sheets lined with silicone mats. Whisk together the egg and water to make the egg wash, then brush the croissants with it. Allow them to rise in a warm area for about 45 to 60 minutes.

Preheat the oven to 400 degrees F (200 degrees C). Brush the croissants gently but thoroughly again with the egg wash.

Bake in the preheated oven until beautifully browned, about 25 minutes. Transfer the croissants to a cooling rack and let them cool to room temperature before serving.