Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, whisk together the flour, baking powder, salt, and 1 tsp cinnamon. Set aside.

In a large bowl, cream the softened butter with the granulated sugar and ½ cup brown sugar until the mixture is light and fluffy—about 2–3 minutes with a mixer or 4–5 minutes by hand.

Beat in the egg and vanilla until fully incorporated and smooth.

Add the dry ingredients to the wet in two additions, stirring gently until just combined. Don’t overmix; you want a soft, slightly tacky dough.

In a small bowl, combine ½ cup brown sugar and 2 tsp cinnamon for the filling.

Place half of the dough on a sheet of parchment paper and press or roll it into a rectangle roughly 1/4-inch thick. Sprinkle the cinnamon-sugar filling evenly over the dough.

Roll the dough up tightly from one long side into a log, using the parchment to help lift and roll. Repeat with the remaining dough and filling.

Use a sharp knife or unflavored dental floss to slice each log into 1/2-inch thick rounds and place on the prepared baking sheet about 1 inch apart.

Bake for 10–12 minutes, until the edges are just golden and the centers are set.

Cool on the baking sheet for 5 minutes, then transfer to a wire rack to finish cooling.