Let the butter rest at room temperature for about 30 minutes. Place between two sheets of wax paper. Using a rolling pin, pound, roll, and shape the butter into an 8" square.  Wrap in wax paper and chill until cold.

In a large mixing bowl or the bowl of an electric mixer, combine 1 c. flour with 1 c. lukewarm water and 1 tsp. dry active yeast.  Stir until the lumps are dissolved, cover with a tea towel, and let rise for 1 hour to make a sponge.

Add the rest of the flour, salt, and milk to the risen sponge mixture. Stir to combine, and then knead by hand or with an electric mixer until strong, about 10 minutes. Cover and allow to rise for 30 minutes.

Roll the dough into a 9"x18" rectangle, and place the chilled square of butter on one end of it. Fold the dough over the butter to encase it (as in image #1), pinching the edges to seal, and pound/roll piece out to be a 9"x18" rectangle again.

Fold the lower half of the dough up 1/3 of the way, and then the top half over that, like an envelope (as in image #2). Rotate 90 degrees to the right (so that the folded edge of the dough is to your left), and roll the dough out again into a rectangle (same size again). Fold up, envelope style, again (as in image #3). If the dough is getting warm or difficult to work with at this point, cover, and let it chill for at least 20 minutes or until cold.

Repeat the last process again; roll (as in image #3) into a rectangle, fold into an envelope, rotate, roll, and fold again (as in image #4). Wrap the folded piece of dough in plastic and refrigerate for 20-30 minutes.

Remove the cold dough from the refrigerator and roll out on a lightly floured surface into a 9"x18" rectangle (as in image #5). Cut the dough in half lengthways, and then into 12 triangles, with the base of each one being about 5 inches in width (as in image #6).

To shape the croissants, cut a little slit into the base of the triangle, roll the edges out towards the sides, and roll up, wide end to short end. Make sure the tip of the triangle is tucked underneath, and curve the edges around to form a half moon shape (or just leave them in a straight, rolled croissant if you prefer).

Cover the shaped croissants with a tea towel and allow to rise for 1-3 hours, or until doubled. Preheat the oven to 400 degrees F.

Place the pan of croissants into the oven, reduce the temperature to 375 degrees, and bake for 25-35 minutes, or until golden brown. Cool on wire racks.