Mix water, yeast, and 1 tablespoon sugar in the bowl of a stand mixer. Let sit 5–10 minutes until foamy.

Add flour (fluff before measuring), remaining sugar, salt, and melted butter.

Mix on low until a shaggy dough forms. Continue mixing 3–4 minutes. Dough should be soft and slightly sticky. Avoid developing too much gluten. Cover with a damp towel or oiled plastic wrap and refrigerate 2–3 hours until doubled.

Place 2 sticks + 2 tablespoons butter on lightly floured parchment. Cover with a second parchment sheet. Beat with a rolling pin into an ~8×8-inch square.

Wrap butter in plastic wrap and refrigerate. Remove 10–15 minutes before rolling dough so it stays cool but pliable.

Punch down risen dough gently. Turn onto a very lightly floured surface. Roll into a 10×16-inch rectangle.

To Laminate the Dough: Place butter square on the left half of dough. Fold right half over to fully enclose butter. Leave about a 1-inch dough border around the square of butter. Lightly seal edges by gently pressing them together.

Roll dough with enclosed butter back into a 10×16-inch rectangle. Be careful that no butter squeezes out of the edges.

Croissant layers form through repeated rolling and folding. There are 2 main types of folds: Envelope Fold- Fold the dough into thirds like a letter.

Book Fold- Fold both ends of your dough to the center, then fold again like closing a book. Use these folds for the following steps.

Perform an envelope fold on the 10×16-inch dough rectangle. After folding, wrap lightly in plastic wrap. Refrigerate 20–30 minutes to chill the butter and relax the gluten. (At this point, you will have 3 butter layers.)

After chilling, remove the dough, rotate 90 degrees from its previous position on your table, roll again to 10×16 inches. Keep layers intact and try to prevent butter leakage.

Perform a book fold. Wrap and refrigerate 20–30 minutes. (You'll now have 12 butter layers.)

After chilling, remove dough, rotate 90 degrees again, and roll to 10×16 inches.

Perform another envelope fold. Wrap and refrigerate overnight (8–12 hours) for bulk fermentation. (36 butter layers.) This improves texture and flavor.

To Cut, Shape, and Bake: Remove dough from fridge. Place on a lightly floured surface. Roll into a 12×26-inch rectangle. Trim 1 inch from each side to create a 10×24-inch rectangle.

Cut vertically every 4 inches across the width, creating six rectangles (4 inches wide × 10 inches tall).

Cut each rectangle diagonally corner to corner with a pizza cutter to form 12 equal triangles.

Cut a 3 cm slit in the center of each triangle’s wide base toward the tip. Spread slightly and roll toward the point into a spiral. Do not roll tightly.

Place six croissants per cookie sheet on two sheets. Cover with a damp cloth. Proof 1½–2 hours in a cool spot until slightly wobbly. Avoid warm areas to prevent butter leakage.

Preheat oven to 400°F.

Whisk egg with 1 tablespoon water. Brush tops and sides lightly.

In a small heat-resistant bowl, mix sugar and lemon zest. (This will help draw the oils out of the zest for maximum flavor.) Let rest for 5 minutes.

Once the sugar and zest are finished resting, stir the lemon juice into the mixture until combined.

Next, crack both eggs and mix them very well into the sugar and lemon juice. Try to break up as much of the whites as you can.

Once fully combined, place a small saucepan filled with 3 inches of water on the stove and turn it to high heat until the water gently boils. Once the water boils, gently set your heat-resistant bowl on top of the pot with the boiling water. (The bowl should not be in the water, but resting over it. Allow the steam from the water to hit the bottom of the bowl and slowly bring your lemon curd up to temperature). This is called a double boiler.

Stir your lemon mixture vigorously the entire time it is cooking to avoid getting lumps of cooked egg. You will know the lemon curd is finished cooking when it thickens up and coats the back of your spoon.

Once cooked, remove the lemon mixture from the heat and place it into the fridge to cool completely.

Once cool, move on to make the marshmallow meringue.

Once again, place a small pot filled with 3 inches of water on the stove to prepare a double boiler.

Once the water has boiled, place your heat resistant bowl over the top of the water, and slowly heat your egg whites and sugar, whisking the entire time. You do not want to cook the eggs. You are only looking for the sugar to dissolve (completely) and the egg whites to get slightly warm. Once the sugar has dissolved, remove from heat.

Immediately place your warm egg white mixture into the bowl of a clean stand mixer with the whisk attachment (if you do not have a stand mixer, you can use a clean bowl and an electric hand mixer), and whisk on high until medium, glossy peaks form. Turn off mixer, and set aside.

Once the marshmallow meringue and lemon curd are both ready, gently place small dollops of lemon curd in with the marshmallow meringue in the mixing bowl.

With a rubber spatula, lightly fold the two fillings together, but do not mix completely. This will cause them to form swirls as they are piped. Gently spoon the filling into a piping bag that is equipped with a filling tip.

Next, pick up one the of croissants, and make an opening in one of the pointed ends with the filling tip until it is about halfway into the croissant. Gently squeeze the pastry bag until the croissant begins expanding slightly, indicating that it is full. Repeat with all 12 croissants.

Once all croissants have been filled, dust lightly with powdered sugar, serve, and enjoy!