01 - In a large mixing bowl, whisk together the flour, instant yeast, sugar, and salt. Pour in the lukewarm water, milk, and melted butter, stirring until a shaggy dough comes together.
02 - Turn the dough onto a lightly floured surface and knead for 5 to 7 minutes until smooth and elastic. Place in a lightly oiled bowl, cover with a damp towel or plastic wrap, and let rise in a warm spot for 1 hour or until doubled in bulk.
03 - While the dough rises, place the room-temperature butter between two sheets of parchment paper. Using a rolling pin, beat and roll it into a rectangle roughly 6 x 8 inches. Chill in the refrigerator until firm but still pliable.
04 - On a floured work surface, roll the risen dough into a large rectangle approximately 12 x 20 inches. Spread the butter block evenly over the surface. Fold the dough into thirds like a letter, rotate 90 degrees, roll back out to the same dimensions, and fold into thirds again.
05 - Wrap the folded dough tightly and refrigerate for 1 hour to firm the butter layers and relax the gluten.
06 - Roll the chilled dough out once more to a rectangle of about 12 x 20 inches. Using a sharp knife or dough scraper, cut the dough lengthwise into 12 even strips.
07 - Take one strip at a time, gently stretch it if needed, and roll it up tightly from one end. Cut the rolled strip down the center lengthwise to expose the interior layers. Twist each half into a spiral and coil it into a greased muffin tin cavity with the layered side facing outward. Repeat with remaining strips.
08 - Cover the muffin tin loosely and let the shaped cruffins rest at room temperature for 45 to 60 minutes until visibly puffy and nearly doubled.
09 - Preheat the oven to 400°F. Bake the cruffins on the center rack for 18 to 22 minutes until deeply golden brown and well risen throughout.
10 - Allow the cruffins to cool in the tin for 5 minutes. If desired, roll the warm cruffins in a mixture of cinnamon and sugar until evenly coated. Serve warm or at room temperature.