Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking soda, baking powder, and salt. Set aside.
In a large bowl, using an electric mixer, cream the softened unsalted butter and granulated sugar together until light and fluffy, about 3-4 minutes.
Add the egg and vanilla extract to the butter mixture and beat until well combined.
Mix in the sour cream until fully incorporated.
Gradually add the dry flour mixture to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Scoop about 1 1/2 tablespoons of dough and roll it into a ball. Roll each ball in additional granulated sugar to coat.
Place the sugar-coated dough balls onto the prepared baking sheets about 2 inches apart.
Bake in the preheated oven for 9-11 minutes, or until the edges are set and just beginning to turn golden but the centers are still soft.
Remove the cookies from the oven and let them cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.