Prepare the “detrampe” (croissant dough) by combining the flour, sugar, and salt in the bowl of a stand mixer. Add 60g butter and mix together until combined.
Combine the yeast and 125g water in a small mixing bowl, whisk to combine. Add the milk, and whisk again until combined. Let sit for three minutes.
Pour the milk mixture into the dry ingredients and combine using the hook attachment. Do not overmix, or the dough will be difficult to roll and shape.
Using a bowl scraper, and scrape the dough from the bowl into a large bowl and place plastic over the bowl. Place it in the refrigerator for 30 minutes.
Prepare the “beurrage” (butter block). Wrap the cold butter in plastic film, and using the rolling pin, pound on it to soften it until it is 8″ by 12″. Refrigerate it until ready to use.
Remove the bowl from the refrigerator, and using a dough scraper, scrape the dough onto a clean, flat work surface.
Using a rolling pin, roll the dough into a rectangle, 12″ by 18.”
Unwrap the beurrage. It should be 2/3 the size of the dough. Place it on the dough, leaving 1/3 uncovered.
Fold the top third of the uncovered dough over the middle third of the butter. Fold the bottom third of the butter-covereddough up, over, and onto the top of the other two sections of folded dough (It should be folded in thirds like a letter.)
Turn the dough so that it is vertical. Using a rolling pin, gently roll the dough to press it together. This is the end of the “first turn.”
Wrap the dough in plastic and refrigerate it for 30 minutes. Remove the dough from the refrigerator and place it on the work space so that it is vertical. Roll the dough into a long rectangle, about 12″ by 18-24.” Fold the dough like a letter. Wrap in plastic and refrigerate for 30 minutes. This the “second turn.”
Repeat this process two more times, for a total of four turns.
Line baking sheets with parchment paper. Unwrap the dough and roll it into a rectangle, 12″ by 24.” Using a knife or a croissant cutter, cut the dough into 24 triangles.
Make a small, one-half inch slit in the center of the base of each triangle. Fold the two tabs that are formed by the slit up and toward the outside edges. Roll the bottom up towards the top of the triangle, and continue rolling. Carefully bend the finished croissant into a crescent shape. Work quickly to keep the dough from getting too warm.
Place the finished croissants on the prepared baking sheets. Cover with plastic and place in a warm, draft-free spot for one hour. They should double in size.
Preheat the oven to 350F. Bake the croissants for 20-25 minutes, or until golden brown all over. Serve them immediately.