In the bowl of a mixer, add the milk, brown sugar, and yeast and stir it with a fork slightly.
Add the flour and salt to the bowl. Using the dough hook, mix on low speed for about 5 minutes until the dough is smooth and very soft. If more flour is needed because the dough is too sticky, add it about 1 Tbsp. at a time. Remove dough from the mixing bowl and knead for a couple more minutes on your working surface. Place dough back in the bowl, wrap with plastic wrap, and refrigerate for 1 hour.
While the dough is chilling, prepare the butter. Arrange the sticks of butter horizontally on a piece of wax paper. Cover the butter with another piece of wax and pound and roll out on both sides until the butter forms a nice 8x5-inch rectangle. Cover with plastic wrap and refrigerate until ready to use.
Flour your work surface lightly, then roll out the dough into a big rectangle that’s about 16x10 inches. Place the butter directly in the center of the dough and fold the dough as you would a letter, bottom third of dough over butter, then top third down over the dough. If you have any excess flour, brush it off. Turn the dough so that the short side is nearest you and start rolling it into another 16x10-inch rectangle. Fold in thirds like a letter again. This was the first fold. Wrap it up in plastic wrap and chill for another hour.
Repeat as above. With the short side near you, start rolling until you get another 16x10-inch rectangle. Fold it in thirds again, then wrap and chill for another hour. Repeat this 3 more times so that it will make a total of 5 folds. After the last fold, refrigerate overnight or at least 8 hours.
Cut the dough in half, and freeze half if you’re only going to use half of it. Roll out each piece of dough into a long rectangle, so that it’s about 1/4 of an inch in thickness. Using a pizza cutter, cut each square into 4 triangles. Using one triangle at a time, start rolling from the wide side, while at the same time stretching the end of the triangle. Continue rolling the croissant, and as you’ll notice because you stretched it into a long piece, you’ll be able to roll the croissant a few times. Repeat this with remaining dough and place the croissants on an ungreased baking sheet, with about 1-2 inches in between them. Let the croissants sit for another hour – you’ll notice they’ll rise a bit, then brush them with egg wash.
Preheat oven to 400°.Place the baking sheet in the oven and bake the croissants for 8-12 minutes, then turn down the heat to 375° and bake them for another 8-12 minutes, until golden brown.