In a large bowl fitted with a dough hook, stir together the warm milk, brown sugar, and yeast.

Let stand until foamy, about 5 minutes.

Add 3 3/4 c. flour and the salt, and turn the mixer to low speed.

Beat until dough is smooth and soft, 6-7 minutes.

On a lightly floured surface, knead dough by hand for 1-2 minutes, adding more flour as needed to produce a soft, slightly sticky dough.

Form it into a 2-inch thick rectangle, wrap it in plastic wrap, and refrigerate it until chilled, about 1 hour.

On a large piece of parchment paper, arrange the 3 sticks of butter adjacent to each other, sides touching.

Top with a second large piece of parchment paper.

Using a rolling pin, pound and roll the cold butter into a uniform 8x5-inch rectangle.

Once it measures 8x5 inches, place it in the refrigerator to chill while you roll out the dough.

Unwrap the dough onto a lightly floured surface.

Gently stretch and knead the dough into a 16x10-inch rectangle, careful not to overwork it.

Remove the butter slab from the fridge.

With the shortest side of the dough near you, unwrap the butter slab and place it in the center of the dough so that the long sides of the butter slab are parallel to the short sides of the dough.

Fold the dough over the butter as you would a letter - fold the bottom third of the dough over the butter, then the top third over that dough.

Again with the short side near you, use the rolling pin to flatten the dough slightly by pressing down with it horizontally across the dough at regular intervals. Then roll the dough into a 15x10-inch rectangle.

Fold the dough in thirds, like a letter (as above), and form a 10x5-inch rectangle. This process completes the first 'fold'.

Wrap the dough rectangle in plastic wrap, and return it to the refrigerator. Chill for 1 hour.

Repeat this folding process 3 more times: roll it into a 15x10-inch rectangle using flour as necessary to keep it from sticking, fold it like an envelope in thirds, and form a 10x5-inch rectangle. After each fold, refrigerate the dough for 1 hour. You'll complete a total of 4 folds.

Wrap the dough tightly in plastic wrap, and refrigerate for at least 8 hours, but no more than 24 hours (after which, the dough may not sufficiently rise when baking).

Ready to roll and bake! Cut the dough in half, and chill one half while working with the other.

On a lightly floured surface, roll out that half to a 16x12-inch rectangle. Trim edges with a pizza wheel or sharp knife so that it's a uniform, clean rectangle.

With the shortest side near you, cut the dough in half horizontally. Cut those halves vertically into thirds, forming 6 rectangles. Then cut each of those 6 rectangles diagonally. It will form 12 triangles.

Now we'll use our hands to form each triangle into a croissant. Hold 1 triangle, and lightly stretch it with your hands to elongate it by about 30%. Roll the triangle from the long side to the tip, and make sure to tuck and pinch the tip to the bottom of the croissant. If the tip isn't on the bottom, the croissant will unroll and open up while baking.

Place the croissant, tip side down, on a parchment paper or silicone mat-lined baking sheet.

Repeat with remaining triangles, then repeat the rolling/cutting process with the remaining dough half in the fridge, arranging croissants two inches apart on the baking sheets.

Let croissants rise for 1 hour.

Adjust oven racks to upper and lower thirds, and preheat oven to 400 degrees.

Brush croissants with melted butter.

Bake at 400 degrees for 10 minutes, then switch the position of the sheets in the oven AND rotate sheets 180 degrees.

Reduce oven to 375 degrees, and continue baking until croissants are golden, about 7-8 minutes.