Preheat your oven to 400°F (200°C). Generously grease a standard 12-cup muffin tin.

On a lightly floured surface, roll out the thawed puff pastry into a 10x14-inch rectangle. Spread the 2 tablespoons of softened butter over the surface. In a small bowl, combine the light brown sugar and 1/2 teaspoon of cinnamon. Sprinkle this mixture evenly over the butter.

From a long edge, roll the pastry into a tight log. Trim the ends and cut the log into 12 equal pieces.

Take each piece and roll it up like a snail shell, tucking the tail end underneath. Place each shaped cruffin into a prepared muffin cup.

Bake for 15-20 minutes, until the cruffins are puffed and a deep golden brown. Let them cool in the tin for 5 minutes before transferring to a wire rack.

While the cruffins are still warm, brush them all over with the 4 tablespoons of melted butter. In a shallow bowl, combine the granulated sugar and the remaining 1 teaspoon of cinnamon. Roll each buttered cruffin in the mixture to coat completely.

Transfer the dulce de leche to a piping bag fitted with a filling tip. Insert the tip into the center of each cruffin and fill. Serve immediately.