01 - In a large mixing bowl, whisk together the flour, instant yeast, sugar, and salt. Pour in the lukewarm water, milk, and melted butter. Stir with a wooden spoon or dough whisk until a shaggy dough forms and no dry flour remains.
02 - Turn the dough onto a lightly floured surface and knead for 5 to 7 minutes until smooth, springy, and elastic. Shape into a ball, place in a lightly oiled bowl, cover with plastic wrap or 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. Using a rolling pin, beat and roll it into a rectangle approximately 6 x 8 inches. Refrigerate until needed but remove about 10 minutes before laminating so it stays pliable, not hard.
04 - On a floured work surface, roll the risen dough into a large rectangle about 12 x 20 inches. Place the butter block on one half of the dough and fold the other half over to enclose it. Roll out again to 12 x 20 inches. Fold the dough into thirds like a business letter. Rotate 90 degrees, roll back out to the same dimensions, and fold into thirds once more. Wrap tightly and refrigerate for 1 hour.
05 - Remove the dough from the refrigerator. Roll it out on a floured surface into a large rectangle about 12 x 20 inches. Using a sharp knife or dough scraper, cut the dough lengthwise into 12 even strips approximately 1 inch wide each.
06 - Working with one strip at a time, gently stretch it slightly if needed and roll it up tightly from end to end into a compact spiral. Using a sharp knife, cut the rolled strip straight down the center lengthwise to expose the buttery layers inside.
07 - Take each cut half and twist it into a loose spiral, then coil it up and nestle it into a greased muffin tin cavity with the cut layers facing outward. Repeat with all remaining halves to fill all 12 cups.
08 - Cover the muffin tin loosely with a damp towel or oiled plastic wrap. Let the shaped cruffins rest at room temperature for 45 minutes to 1 hour until visibly puffed and nearly doubled in size.
09 - Preheat the oven to 390°F (200°C). 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 if needed.
10 - Cool the cruffins in the tin for 5 minutes, then turn them out onto a wire rack. While still warm, roll each cruffin in the cinnamon sugar mixture if desired. Serve warm or at room temperature.