Preheat your oven to 375°F (190°C). Grease a standard muffin tin with butter or non-stick spray.
In a small bowl, mix together the granulated sugar, ground cinnamon, nutmeg, and sea salt. Set this mixture aside.
On a clean surface, unfold one sheet of puff pastry and roll it out gently to smooth it. Brush the surface with melted butter and sprinkle a generous amount of the cinnamon-sugar mixture evenly over the pastry.
Repeat the process for the second sheet of puff pastry.
Starting from one edge, roll the first sheet of pastry tightly into a log to create a spiral. Cut the log into 6 equal pieces.
Take each piece and place it vertically in a muffin cup, with the outside of the roll facing out. Repeat this step with the second pastry sheet.
In a small bowl, whisk the egg and brush it over the top of each cruffin. This will give them a beautiful golden color as they bake.
Sprinkle any remaining cinnamon-sugar mixture over the tops of the cruffins.
Bake in the preheated oven for 25-30 minutes or until the cruffins are puffed up and golden brown.
Allow them to cool in the muffin tin for 5 minutes before transferring to a wire rack. Optionally, dust with powdered sugar before serving.