Preheat the oven to 400°F and line a baking sheet with parchment paper.

Lay one pastry sheet flat and spread with half the butter, leaving a 1-inch border.

Mix brown sugar and cinnamon, sprinkle half over the buttered sheet.

Repeat with the second sheet, remaining butter and remaining cinnamon sugar.

Stack the two sheets with filled sides matching, and roll gently to seal them together.

Roll the stacked pastry into a tight log from one long side.

Curve the log into a ring on the pan and pinch the ends together to close it.

Snip shallow angled slashes around the ring about 1 inch apart with kitchen shears; this is what makes it look braided once it puffs.

Brush with beaten egg and bake 22 to 25 minutes, until deeply golden and puffed.

Cool on the pan 20 minutes; puff pastry collapses if moved too soon.

Whisk powdered sugar and milk to a thick icing, drizzle over the cooled ring, and band with purple, green and gold sugar before it sets.