Cream the softened butter and sugar until light and fluffy, about 3 minutes, then scrape the bowl to blend evenly. Beat in the egg and vanilla until smooth.

Whisk together the flour, baking powder, and salt in a separate bowl, then gradually mix into the butter mixture until a soft dough forms. If sticky, add flour a tablespoon at a time.

Divide the dough in half, wrap each piece in plastic, and chill for 30 minutes until firm. In a small bowl, mix melted butter, brown sugar, and cinnamon into a smooth spread.

Roll each dough half into a 10×8-inch rectangle. Spread the cinnamon mixture over one, top with the other, and press gently. Roll tightly from the long side into a log, seal, wrap, and chill for 15 minutes.

Preheat the oven to 350°F (175°C). Slice the dough into ¼-inch rounds, arrange on parchment-lined sheets, and bake for 10–12 minutes until golden at the edges.

Cool on the sheet for 5 minutes, then transfer to a rack. Dust with powdered sugar or pearl sugar while slightly warm.