Twenty-four hours before serving, in the bowl of a stand mixer fitted with the dough hook, combine the flour, sugar, salt, and yeast.

Create a well in the center and pour in the water and milk. Mix on low speed until a tight dough comes together around the hook, about 5 minutes. Cover with a damp towel and set aside for 10 minutes.

Reattach the dough hook, mix on medium-low speed, and add the butter pieces all at once until the dough is very smooth and stretchy, 8 to 10 minutes.

Form the dough into a ball, place seam-side down on a floured surface, and cut two deep perpendicular slashes in the dough.

Place slashed-side up in the mixing bowl, cover with plastic wrap, and let rise until about 1? times its original size, 45 minutes to 1 hour.

Chill in the refrigerator for at least 4 hours and up to 12.

Make the butter block by placing the sticks of butter side-by-side in the center of parchment paper, fold the sides over, and use a rolling pin to flatten into a scant ?-inch thick layer, forming an 8-inch square.

Chill the butter block in the refrigerator.

Eighteen hours before serving, remove the dough from the refrigerator, deflate it, and stretch into a rough square measuring no more than 8 inches.

Place dough on plastic wrap, wrap it up, then freeze for 20 minutes.

Roll the dough into a rectangle measuring 16 inches long and 8 inches wide. Brush off any flour.

Invert the butter block on the center of the dough rectangle, and wrap the dough around the butter.

Rotate the dough 90 degrees, and roll it out into a 24-inch long, ?-inch thick slab. Trim the ends for an even rectangle shape.

Dust off flour, fold the short sides of the rectangle toward the midline, then fold the slab in half crosswise.

Wrap tightly in plastic and freeze for 15 minutes, then refrigerate for 1 hour.

Let dough sit for about 5 minutes, then roll out into a long, narrow ?-inch thick slab. Dust off any excess flour.

Fold the dough in thirds like a letter, press gently, wrap in plastic, freeze for 15 minutes, then refrigerate for 1 hour.

Let the dough sit for about 5 minutes, then roll out into a 14-by-17-inch slab.

Wrap tightly in plastic, freeze for 20 minutes, then chill overnight.

Four and a half hours before serving, arrange oven racks and bring a skillet of water to a simmer. Transfer to the oven for proofing.

Line two baking sheets with parchment paper. Roll out the chilled dough to 17-by-14 inches and cut into four 4-by-14-inch rectangles.

Cut each rectangle into two triangles by slicing from opposite corners. Trim the short side at a slight angle.

Roll each triangle starting from the base, place on the baking sheet, and cover loosely with plastic wrap.

Three and a half hours before serving, place baking sheets in the proofing oven until doubled in size, about 2 to 2? hours.

Remove the baking sheets, chill for 20 minutes, and heat the oven to 375 degrees.

Mix the egg yolk and heavy cream, then brush the mixture over each crescent.

Bake for 20 minutes, then rotate and switch racks, baking until deep brown, another 10 to 15 minutes.

Cool completely on baking sheets.