In a medium bowl, whisk together the flour, baking powder, and fine sea salt. Set aside.

In a large bowl with an electric hand mixer or stand mixer, beat the softened butter and granulated sugar for 2 minutes until creamy and fluffy.

Add the egg and vanilla extract, beating until smooth and fully emulsified.

Gradually add the dry ingredients on low speed, mixing just until a soft, pliable cookie dough forms.

Roll the dough out between two sheets of parchment paper into a 12x9-inch rectangle about 1/4-inch thick.

Brush the surface of the dough with melted butter. In a small bowl, combine dark brown sugar and cinnamon, then sprinkle evenly across the dough right to the edges.

Starting from the long edge, roll the dough tightly into a log using the parchment paper to assist. Wrap tightly in plastic wrap and chill in the refrigerator for at least 45 minutes to firm up.

Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper. Using a sharp knife, slice the chilled log into 1/2-inch thick pinwheels.

Place pinwheels 2 inches apart on the prepared baking sheets. Bake for 10 to 12 minutes just until the edges are lightly golden but the centers remain soft.

Cool on the pan for 5 minutes, then transfer to a wire cooling rack. Whisk together softened cream cheese, powdered sugar, vanilla, and milk until smooth and drizzle over the cooled cookies!