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 greased bowl, cover tightly, 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 an even rectangle approximately 6 x 8 inches. Chill 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 over the dough and spread it evenly. Fold the dough into thirds like a business letter, rotate 90 degrees, roll back out to 12 x 20 inches, and fold into thirds again.
05 - Wrap the folded dough and refrigerate for 1 hour to firm the butter and relax the gluten.
06 - Roll the chilled dough out once more into a 12 x 20 inch rectangle. Using a sharp knife or dough scraper, cut the dough lengthwise into 12 even strips about 1 inch wide.
07 - Take one strip at a time, gently stretch if needed, and roll it up tightly into a spiral. Cut the rolled strip in half 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. Repeat with remaining strips.
08 - Cover the muffin tin loosely with a towel and let the cruffins rest at room temperature for 45 minutes to 1 hour until puffed and noticeably risen.
09 - Preheat the oven to 390°F. Bake the cruffins on the center rack for 18 to 22 minutes until deeply golden brown and well risen. If the tops brown too quickly, tent loosely with foil during the last few minutes.
10 - Cool the cruffins in the tin for 5 minutes, then turn out onto a wire rack. While still warm, optionally roll each cruffin in a mixture of cinnamon and sugar until evenly coated. Serve warm or at room temperature.