Step 1: Preheat your oven to 400°F (200°C) and liberally grease a standard muffin tin with melted butter.
Step 2: On a lightly floured surface, roll out one sheet of puff pastry into a large rectangle, roughly 10×12 inches.
Step 3: Spread half of the Nutella in a thin, even layer across the pastry, leaving a 1/2-inch border at the edges.
Step 4: Starting from the long edge, roll the pastry into a tight log. Repeat the process with the second sheet of pastry and the remaining Nutella.
Step 5: Using a sharp knife, cut each log in half crosswise, then slice each half lengthways to expose the internal layers of dough and Nutella.
Step 6: With the cut side facing outwards, roll each strip into a spiral shape (like a rose) and tuck the end underneath. Place each coil into the prepared muffin tin.
Step 7: Bake for 22-25 minutes until the cruffins have risen significantly and are deep golden brown. While baking, mix the sugar and cinnamon in a small bowl.
Step 8: Remove from the oven, let cool for 5 minutes, then carefully remove from the tin and toss in the cinnamon-sugar mixture while still warm.