In a measuring cup or small bowl, combine warm milk, granulated sugar, and active dry yeast. Let sit for 5–10 minutes until foamy.

In the bowl of a stand mixer, combine bread flour, all purpose flour, and salt.

Add the yeast mixture and cold water. Mix until a shaggy dough forms.

Add softened butter and knead for 6–8 minutes until the dough becomes smooth and elastic. The dough should feel slightly tacky but not sticky.

Cover the dough and let rest for 1 hour until slightly puffy.

Shape dough into an 8x10-inch rectangle. Wrap tightly and refrigerate for 1–2 hours or overnight.

Place cold butter between two sheets of parchment paper.

Using a rolling pin, pound and roll the butter into an 8x5-inch rectangle.

The butter should be cold but pliable and evenly flattened. If it feels too hard, lightly pound it again until flexible.

Refrigerate until ready to use.

Roll chilled dough into an 8½x12-inch rectangle.

Place the butter block in the center and fold the dough over the butter, sealing the edges.

Roll dough into an 8x24-inch rectangle.

Fold into thirds like a letter.

Wrap and refrigerate for 30–45 minutes.

Roll dough back into an 8x24-inch rectangle.

Fold into thirds again.

Chill for 30–45 minutes.

Wrap tightly and chill at least 1 hour or overnight, up to 24 hours.

If the butter softens, smears, or starts breaking through the dough at any point, refrigerate until cold again before continuing.

Roll laminated dough into a 10x24-inch rectangle about ⅛-inch thick.

Trim the uneven edges.

Sprinkle half of the cinnamon sugar mixture evenly over the dough.

Cut dough into approximately 2-inch strips.

Gently stretch each strip slightly and then roll into spiral pinwheel and tuck the ends underneath.

Place each cruffin into a parchment lined muffin well.

Allow cruffins to proof at 70–75°F for 2–3 hours until noticeably puffy with rounded edges and a slight jiggle. (Proofing time may take longer if your kitchen is cool. If your kitchen is warm, proof in a slightly cooler area to prevent butter from softening too much.)

Optional: Cover tightly and refrigerate overnight after shaping.

Preheat oven for 40 minutes at 400°F if possible.

Whisk together egg and heavy cream for the egg wash. Brush the tops of the cruffins gently.

Bake at 425°F for 8 minutes.

Reduce oven temperature to 375°F and continue baking for 18–20 minutes until deeply golden brown.

Allow cruffins to cool slightly until comfortable to handle and then roll the warm chugging in the remaining cinnamon sugar mixture.

If desired, fill with Nutella using a piping bag after cooling slightly.

Cool about 10 minutes before serving.