In a large bowl, combine your potato flake sourdough starter, sugar, salt, melted butter, cold milk, and flour.

Stir the ingredients until a shaggy dough forms.

Once the dough is smooth, form it into a ball and place it in a bowl.

Cover the bowl with plastic wrap and let it sit at room temperature for 8-10 hours, or until it nearly doubles in size.

After the dough has doubled, cover it and refrigerate it for at least 2 hours to firm up before lamination.

On a sheet of parchment paper, mark out a 6x8 inch rectangle with a pen or pencil. Pre-fold the lines to form a rectangle shape. Be sure to fold the parchment so the markings are on the outside and won't touch the butter.

Sprinkle ½ tablespoon of flour over the rectangle area and evenly distribute the cold butter (cut into small pieces) across the flour.

Sprinkle the remaining ½ tablespoon of flour on top of the butter.

Fold the parchment over the butter, using your markings as a guide.

Flip the pouch over to keep the edges closed. Then use a rolling pin and your fingers to evenly press the butter into the pouch to make a butter block. Chill if butter has begun to melt and looks greasy on the edges. If butter is still cold but pliable when you bend the block, it is ready for the next step.

After the dough has chilled, turn it out onto a lightly floured surface. Use your hands to begin to shape the dough into a rectangle and pull the corners to shape them. Roll it into a 13x9-inch rectangle. Dusting the top and bottom with flour as needed to prevent sticking.

Unwrap the butter block and place in the center of the dough, with a short side facing you.

Fold the edges of the dough over the butter so they meet in the center, fully encasing the butter block. Seal the edges well to prevent the butter from escaping during rolling. Brush away loose flour with a pastry brush or your hands.

With the dough positioned so that the seam is parallel to you, use your rolling pin to roll it into a 24x10-inch rectangle. Try to keep the edges and corners straight. Dust underneath with more flour as needed to prevent sticking.

Fold the short ends of the rectangle inward to meet off center. (You don't want them to meet directly in the center because this will cause it to open up in the next fold) Then fold the new ends together like you're closing a book. Brush away any loose flour as you go. This is your first lamination.

Wrap the dough in plastic wrap and refrigerate for 20 minutes.

After the dough has chilled, Place dough on your lightly floured surface again, this time with the fold facing you. Press with the rolling pin and roll to a 24x10-inch rectangle again. Dusting with flour as needed to prevent sticking.

This time, fold the short ends of the rectangle in thirds, as if you are folding a letter. Brush off any excess flour to maintain a smooth texture.

Wrap the dough again and refrigerate for 30 minutes.

Remove the dough from the fridge. With the folded side facing you, roll the dough out to a rectangle measuring about 18x11.5 inches. Use a pizza cutter to trim the edges so that they are straight, if needed.

Cut the dough into 5 equal rectangles, measuring to ensure accuracy. I make small cuts as I measure to track where I need to make my cuts. Now, cut each rectangle in half diagonally to form 10 triangles.

Using the pizza cutter, cut a small slit at the base of the large end of each croissant triangle. Gently stretch the corners of dough at the corners and roll the triangle tightly (stating at the larger end) into a croissant shape.

Lightly press the tip of the triangle into the croissant to help it adhere to the underneath side. Repeat for remaining triangles.

Place the croissants on two parchment paper-lined baking sheets, with 5 croissants on each sheet.

One large baking sheet can be used, but they might end up touching during the rising time.

Cover the croissants loosely with plastic wrap and allow them to proof at room temperature for 8-12 hours. They should be wobbly and have visible layers when ready to bake. You can spray your plastic wrap with cooking spray if you are worried about it sticking to the croissants.

You don't want to proof them in a warm place because this could cause the butter to melt out.

I like to let mine rise in the oven with the light off. This is a safe place that is draft free and won’t allow any gnats to get to the rising dough. Allow them to rise until doubled. This took my croissants 11 hours.

Don’t rush this part of the process. Under proofed croissants will leak out butter and won't rise properly in the oven

You should begin to see some separation in the layers when proofing is finished.

Once the croissants have doubled, preheat your oven to 425°F.

Beat your egg and milk together to make an egg wash. Use a pastry brush to brush egg wash over each proofed croissant.This helps give them that shiny, golden finish.

Bake one sheet at a time on the center rack, for 15-17 minutes or until deeply golden brown.

Serving and Storing Potato Flake Sourdough Croissants

Once baked, transfer your croissants to a cooling rack to allow them to cool slightly before serving. They can be enjoyed warm from the oven, with their crispy exterior and soft, buttery interior, or stored for the next day.

Croissants can be stored in an airtight container at room temperature for up to two days, or they can be frozen for up to a month.

To reheat frozen croissants, simply pop them in a preheated 475°F oven for 3-5 minutes, or until they’re warmed through and crispy again.