In a large bowl or the bowl of a stand mixer, combine flour, sugar, yeast, and salt. Add the warm milk and melted butter. Mix until a shaggy dough forms, then knead on a floured surface for 8-10 minutes (or with a dough hook for 5-7 minutes) until smooth and elastic. Place in a greased bowl, cover, and let rise for 1-2 hours, or until doubled in size.

While the dough rises, prepare the butter block. Place the 3 sticks of cold butter between two sheets of parchment paper. Pound with a rolling pin to flatten and shape it into an 8x8 inch square. Refrigerate until firm.

Punch down the risen dough and roll it out on a floured surface to a 16x8 inch rectangle. Place the chilled butter block on one half of the dough. Fold the other half over the butter and pinch the seams to seal. This is the first 'turn'.

Roll the dough into a long rectangle again, about 24x8 inches. Perform a letter fold (folding in thirds). Wrap in plastic and chill for 30 minutes. Repeat the rolling, folding, and chilling process two more times for a total of three turns. After the final turn, chill the dough for at least 1 hour or overnight.

On a floured surface, roll the final chilled dough into a large rectangle (approx. 12x18 inches). Brush with melted butter. Mix the brown sugar and cinnamon, then sprinkle it evenly over the dough.

Tightly roll the dough into a log from the long side. Trim the ends and slice the log into 12 equal pieces.

Grease a standard 12-cup muffin tin. Place each dough slice into a cup, cut-side up. Cover loosely with plastic wrap and let them proof in a warm spot for 1-2 hours, until they are puffy and have risen over the top of the tin.

Preheat your oven to 400°F (200°C). Bake the cruffins for 20-25 minutes, or until deeply golden brown and cooked through. Let them cool in the tin for 5 minutes before transferring to a wire rack.

While the cruffins are still warm, brush them with the remaining melted butter and generously roll them in granulated sugar. Serve immediately for the best experience.