Day 1 In a large mixing bowl at least twice the size of your mixture, combine 50g (3⅓ tbsp) flour and 50g (3⅓ tbsp) water and mix with a spatula until evenly com- bined. Loosely cover with a dish towel or cheesecloth and leave at room temperature spot for 24 hours.

Day 2 Add another 50g (3⅓ tbsp) flour and 50g (3⅓ tbsp) water, mix with spatula to combine. Loosely cover and leave at room temperature for another 24 hours.

Day 3: Add another 100g (6⅔ tbsp) flour and 100g (6⅔ tbsp) water, mix with spatula to combine. Loosely cover and leave at room temperature for another 24 hours.

Day 4: Remove 20 percent of the levain mixture from the container and discard. Loosely cover and leave at room temperature for another 24 hours.

Day 5: Check if your levain is ready to use. It should be light, bubbly, and fluffy, and have a pronounced fermenta- tion aroma without any acidity. If it’s not quite there, “feed” the levain again each day with equal parts flour and water that’s equal to the weight of the levain, until it’s ready.

In a small bowl, stir together the yeast and room temperature water until dissolved. Combine the flour, butter, sugar, egg, cream, salt, 68g levain, and yeast mixture in a stand mixer fitted with a dough hook. Start mixing on the lowest speed and mix for 1 minute, then increase the speed to medium and mix about 3 to 4 minutes more, until the dough is just combined. When finished, the dough will be rough and have very little gluten development. It will also be elastic and come out of the bowl as one piece.

Lightly grease a medium bowl with nonstick spray. Transfer the dough into the bowl and cover with plas- tic wrap pressed directly on the dough, to prevent a skin from forming. Proof the dough in a warm spot until doubled in size, 1 hour 30 minutes to 2 hours.

Remove the plastic wrap and punch down the dough by folding the edges into the center, releasing as much of the gas as possible. Invert the bowl of dough and allow the dough to fall onto a piece of plastic wrap, then shape the dough into a 10-inch (25cm) square. Place the dough, still on the plastic wrap, on a sheet pan and cover with another sheet of plastic wrap. Refrigerate overnight.

Draw a 7-inch (18cm) square on a piece of parchment paper with a pencil. Flip the parchment over so the butter won’t come into contact with the pencil marks. Place the softened butter in the center of the square and cover with another sheet of parchment paper. Use an offset spatula or bench scraper to spread the butter evenly to fill the square. Refrigerate overnight. Tip: It’s important that the butter is truly softened to make forming the butter block easy. Once perfectly room temperature, the butter will be spreadable and have the consistency of cream cheese.

Remove the butter mixture from the refrigerator and let stand for 5 to 10 minutes to become pliable enough to work with. It should still be soft enough to bend slightly without cracking. If it is too firm, gently beat it with a rolling pin on a lightly floured work surface until it becomes pliable. Make sure to press the butter back to its 7-inch (18 cm) square after working it.

Lightly flour your work surface. Remove the dough from the refrigerator, making sure it is very cold throughout. Place the dough on the work surface. Arrange the butter block in the center of the dough so it looks like a diamond in the center of the square (rotated 45 degrees, with the corners of the butter block facing the center of the dough sides). Pull the corners of the dough up and over to the center of the butter block. Pinch the seams of dough together to seal the butter inside. You should have a square slightly larger than the butter block.

Lightly dust the work surface with flour to ensure that the dough won’t stick. With a rolling pin, using steady, even pressure to roll out the dough from the center so that it triples in length. This will take several passes and you may need to add more flour in between rolling to keep the dough from sticking to the surface and rolling pin. When finished, you should have a rect- angle about 20 by 10 inches (50 by 25 cm) and ¼ inch (6 mm) thick.

Place the dough so the shorter sides run left to right. From the top side, fold one-third of the dough onto itself, keeping the edges lined up with each other. From the bottom side, fold the remaining one-third of dough on top of the side that has already been folded. Line up all the edges so that you are left with a smaller rectangle. This technique is called a “letter fold,” since the dough is folded as if it were a piece of paper going inside an envelope. Wrap the dough tightly in plastic wrap and place on a sheet pan. Re- frigerate for about 1 hour to relax the gluten.

With the seam always facing to the right, repeat steps 3 and 4 for your second and third folds. After the third fold, refrigerate the dough for 1 hour.

Lightly flour the work surface and lay the dough flat. Trim about ½ inch of dough from each side to make a neat rectangle. Using a ruler, start from the left side and score the dough every 3 inches (8 cm) along the bottom edge until you reach the right side of the dough. Make the first score on the top edge 1½ inches (4 cm) from the left end. Continue scoring the top edge every 3 inches (8 cm). These staggered marks should give a nice guideline for cutting triangles. Use a large chef’s knife to connect each score mark on the top with the two at the bottom on either side of it. The isosceles triangles should measure 3 inches (8 cm) wide and 10 inches (25 cm) long. There will be narrow triangles of dough left over at each end. Place the cut triangles on a parchment paper-lined sheet pan, wrap tightly in plastic wrap, and refrigerate for 30 minutes to 1 hour.

Remove the dough triangles from the refrigerator, and make sure there is no flour on your work surface. Working with one triangle at a time, hold the base of the triangle with one hand and use the fingertips of your other hand to lightly grasp the triangle near its base and gently stretch it an additional 2 to 3 inches (5 to 8 cm) in length, pulling your fingers toward the tip and being careful not to tear the dough. Tip: Stretching out the dough not only gives you more to roll, it also relaxes the dough.

Starting at the wide end, roll the croissant dough to- ward the tip, keeping steady and even pressure as you roll, until it comes to a rest on the tip of the triangle. When finished, make sure the tip of the dough is on the bottom of the croissant or else it will unravel in the oven. Line a sheet pan with parchment paper. Place the croissants on the sheet pan about 4 inches (10 cm) apart. Lightly lay a piece of plastic wrap over the croissants and refrigerate overnight.

Remove the tray of croissants from the refrigerator. Keep them lightly covered in plastic wrap. Let stand at room temperature until tripled in size, about 2 to 3 hours.

Place a rack in the center of the oven and preheat the oven to 375°F (190°C) for conventional or 350°F (175°C) for convection. In a small bowl, make the egg wash by whisking together the eggs, salt, and milk. Gently remove the plastic wrap from the croissants. Lightly brush the croissants with the egg wash, mak- ing sure not to apply too much pressure to prevent deflating the croissants. Bake on the center rack for 12 to 15 minutes until golden brown. Remove from the oven and let cool briefly.