Ever wanted to make your own croissants or their chocolatey bretheren, pain au chocolat? Now you can! After you've made the base dough, you don't have to cut and shape it right away—you can freeze and store it for later use. Use the base dough to make either variation of this classic treat!

Preparation

For the dough, combine flour, sugar, salt, yeast, water, and milk in the bowl of a stand mixer fitted with a dough hook attachment. Mix on low speed until well combined, about 3 minutes. Add butter and continue to mix on low speed until the butter is well incorporated and no lumps remain, about 3 minutes. Increase mixer speed to medium and mix until the dough is smoother in texture, about 3 minutes. Remove dough from bowl, wrap in plastic wrap, and place in refrigerator to chill for at least 4 hours.

For the butter block, prepare two large sheets of parchment paper. Place butter on one piece, and lay the other piece on top of the butter. Using a rolling pin, whack the chilled butter until it is malleable and spreadable, but still cold. Using the rolling pin, continue to roll out and form the butter into an 8x8-inch square. Fold the parchment to fit the square and press the butter into the corners. Press down on the butter block with a cutting board to ensure uniform thickness. Set the parchment paper-wrapped butter block in the refrigerator.

Remove dough from refrigerator and set it on a lightly floured surface. Using a rolling pin, gently shape dough into a square shape before rolling it out into a 8x14-inch rectangle. Remove butter block from the refrigerator and place it in the center of the dough. Fold the edges of the dough over the butter block, pressing them together to completely seal in the butter. Turn dough 45 degrees, back to its original orientation.

With a rolling pin, roll out the dough, seam-side up, into an 8x14-inch rectangle. Fold the dough in thirds by folding the top third down, followed by the bottom third up. Rotate the dough 90 degrees clockwise. Again, roll out the dough into an 8x14-inch rectangle and repeat the folding process. Wrap dough in plastic wrap and place in the refrigerator until chilled and well rested, at least 1 hour.

Remove dough from the refrigerator and repeat the folding process. Wrap the dough in plastic wrap and let it rest in the refrigerator for 1 more hour. 

Remove dough from the refrigerator and repeat the folding process once more. Wrap the dough in plastic wrap and let it rest in the refrigerator for 4 hours or up to overnight. 

Remove dough from the refrigerator. With a rolling pin, roll out the dough to ⅛–¼-inch thick. Trim off about ¼ inch on all four sides—this helps ensure that it puffs properly in the oven.

Prepare a baking sheet with parchment paper.

For croissants, use a pizza cutter to cut dough vertically into equal thirds. Cut each third diagonally to make triangles. Cut a small notch at the base of each triangle and tug at each side of the base, then tug at the tip of each triangle to stretch it out a bit. Start at the base of the triangle to roll it up and make a croissant shape, being careful not to roll too tightly. Repeat for all triangles.

For pain au chocolat, use a pizza cutter to cut dough into 4x8-inch rectangles. Place a chocolate baton horizontally near the top of each rectangle. Roll the rectangle down into itself once to encase the chocolate baton in dough, then stop rolling and place a second chocolate baton horizontally across the dough and continue rolling. Repeat for all rectangles.

Allow croissants or pain au chocolat to proof covered in a warm area for at least 2–3 hours, until doubled in size.

Preheat oven to 350°F.

For the egg wash, whisk together the egg and milk. Gently brush pastries with egg wash after they have finished proofing.

Place proofed croissants or pain au chocolat on the baking sheet, bake for 16–20 minutes, or until golden brown.