In a small bowl, whisk together the room temperature butter and 3 Tbsp granulated sugar. Add the egg yolk and vanilla extract, then whisk again until smooth.
Add the flour, salt, and baking powder to the bowl. Stir the ingredients until everything is evenly mixed. Place the cookie dough in the refrigerator for about 15 minutes to chill the dough and make it a little more stiff. Begin to preheat the oven to 350 degrees.
While the dough is chilling, stir together the sugar and cinnamon for the cookie topping in a small bowl. Cover a baking sheet with parchment paper (or foil, but be aware that foil will make the cookies brown more on the bottom).
Remove the dough from the refrigerator and divide it into two pieces. Roll each piece of dough into a large ball. Roll each ball in the cinnamon-sugar topping until heavily coated. Place the unbaked cookies at least six inches apart on the baking sheet.
Bake the cookies for 16-18 minutes, or until browned around the edges and slightly golden in the middle. Allow the cookies to cool on a wire rack before eating (they will be soft just after baking, but will firm up upon cooling).