Make the cookie. Start by adding the butter and sugar to the bowl of a stand mixer (or just a bowl to hand mix) and mix on high speed for 1-2 minutes until light and fluffy.
Add the vanilla and egg and mix on medium for another minute.
Combine the salt, baking powder, and flour in a bowl. Add to the butter mixture. Mix just until combined.
Divide the dough into two and wrap in plastic. Chill in the fridge for one hour.
For the filling: combine the sugar, cinnamon, and salt in a small bowl. Leave the melted butter separate.
Preheat the oven to 375°F. On a lightly floured surface or directly on the plastic wrap, roll out one rectangle of dough to about 1/4” thickness.
Spread half the melted butter over it and sprinkle half the sugar mix. Roll tightly, starting with the shorter side. Wrap back in plastic and chill for ten minutes. Repeat for the second rectangle.
Line a baking sheet with parchment paper. Cut 1/2” slices off of the rolled cookie dough and place them at least 2” apart. Bake for 10 minutes, until there is a light golden color. Enjoy!