1 3/4cupsunsalted European-style butter, very cold(395 grams)
1/4cupbread flour(30 grams)
1eachegg yolk
1tablespoonheavy cream
Instructions
In a large bowl or stand mixer, combine the water, milk, instant yeast, and sugar. Stir until the yeast dissolves. Add bread flour, whole wheat flour, salt, and the softened butter. Mix until a dough forms. Knead for about 3-5 minutes until smooth but not sticky.
Cover the bowl and set in a warm place for 30-45 minutes, until slightly puffy but not doubled. Refrigerate for at least 1 hour, or up to overnight.
Take the very cold butter and chop into slices. Arrange these on a piece of parchment paper and sprinkle with 1/4 cup bread flour. Fold the parchment over and pound with a rolling pin until you form an 8-inch square. Chill until firm.
On a floured surface, roll the dough into a 12-inch square. Place the butter block in the center, so it looks like a diamond within the square. Fold each corner of the dough over the butter, encasing it completely.
Roll the dough into a 24×8-inch rectangle. Fold it into thirds like a letter. Wrap and refrigerate for 30-60 minutes to keep the butter cold.
Take out the chilled dough and repeat the rolling and folding two more times (for a total of three folds). Always refrigerate between turns.
Roll dough into a long 8×24-inch rectangle. Cut in half, then cut each half into triangles (about 4.5 inches across at the base). Gently stretch each triangle, then roll from base to tip to form a crescent.
Place croissants on lined baking sheets, with space between them. Cover lightly and let rise at room temperature for 1.5-2.5 hours, until puffy and jiggly.
Preheat your oven to 400°F (200°C). Whisk together the egg yolk and heavy cream, then gently brush over each croissant. Bake for 18-22 minutes until deep golden brown and crisp.
Allow croissants to cool slightly before serving so the crumb sets.
Notes
Keep your butter and dough very cold throughout the process; if you notice the butter softening, pop everything in the fridge.