01 - In a large mixing bowl, whisk together the flour, instant yeast, sugar, and salt. Pour in the lukewarm water, milk, and melted butter, then stir 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 greased bowl, cover with a damp towel, and let rise in a warm spot for 1 hour or until doubled in volume.
03 - While the dough rises, place the room-temperature butter between two sheets of parchment paper. Use a rolling pin to beat and shape it into a rectangle roughly 6 x 8 inches. Refrigerate just until firm but still pliable.
04 - On a floured work surface, roll the risen dough into a large rectangle about 12 x 20 inches. Lay the butter block evenly over the dough surface, then fold the dough into thirds like a letter. Give it a quarter turn, roll back out to the same dimensions, and fold into thirds again. Wrap and refrigerate for 1 hour.
05 - Roll the chilled dough once more into a 12 x 20-inch rectangle. Using a sharp knife or dough scraper, cut the dough lengthwise into 12 even strips approximately 1 inch wide.
06 - Take one strip at a time, gently stretching if needed, and roll it up tightly from end to end. Slice the rolled spiral down the center lengthwise to expose the buttery layers. Twist each half into a loose spiral and coil it into a greased muffin tin cup with the cut layers facing outward.
07 - Cover the muffin tin loosely with plastic wrap and let the shaped cruffins rest at room temperature for 45 to 60 minutes until visibly puffy and nearly doubled.
08 - 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. Rotate the tin halfway through for even browning.
09 - Let the cruffins cool in the tin for 3 to 4 minutes, then turn them out. If desired, roll the warm cruffins in a mixture of cinnamon and sugar. Serve warm or at room temperature.