Whisk the flour, baking powder, and salt together in a medium bowl. Set aside.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter and sugar until completely smooth and creamy, about 2 minutes. Add the egg and vanilla and beat on high speed until combined, about 1 minute.

Add the dry ingredients to the wet ingredients and mix on low until combined. If the dough seems too soft and sticky for rolling, add 1 more Tablespoon of flour.

Divide the dough into 2 equal parts. Roll each portion out in a rectangle onto a floured silicone baking mat (or floured parchment paper) to about ¼ inch thickness. Spread 1 Tablespoon of melted butter onto each rectangle.

Mix the granulated sugar and cinnamon together then sprinkle evenly over each.

Slowly roll up each rectangle into a 9-inch log. Chill the logs of dough for at least 2 hours.

Preheat oven to 350°F (177°C). Line a large baking sheet with parchment paper.

Remove dough logs from the refrigerator and cut into ½ inch slices. Place slices onto baking sheets about 2 inches apart.

Bake for 10-11 minutes, until lightly browned on the sides. Allow to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely before icing.

Whisk all of the icing ingredients together and drizzle over cookies.