Preheat the oven to 375-400 degrees F, positioning a rack in the center of the oven.

Roll the puff pastry to an 18″ long x 14″ wide x ¼” thick rectangle, positioning the long end toward you. Brush any excess flour from the dough. Brush the entire surface of the dough with the egg, making sure to reach the edges.

In a bowl, mix together the brown sugar and cinnamon. Sprinkle evenly over the dough, making sure to reach the edges but leaving a 1″ margin on the far side (long side) of the dough.

Starting with the long side closest to you, begin rolling the dough into a cylinder. When you reach the far end, pinch the dough to form a seam. The cylinder should be about 18″ long. If it isn’t, roll it gently back and forth until it lengthens. Cut the cylinder into 12 equal pieces, each about 1½” wide.

Generously butter a muffin tin and place each piece, cut side up, into a muffin cup. Chill the buns in the freezer for 10 minutes or in the refrigerator for 15 minutes to firm the butter (to create a flakier texture). Bake for 25 minutes, until the buns are golden brown.

Place the granulated sugar in a bowl. Once out of the oven, gently remove the buns from the muffin tin using a tongs rolling each one in the sugar before placing on a silicone mat or parchment paper to cool.*

Serve warm or at room temperature.