Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy clean-up.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. This should take about 3-4 minutes.

Add the egg and vanilla extract to the butter-sugar mixture. Mix until well combined.

In a separate bowl, whisk together the flour, baking powder, salt, and ground cinnamon.

Gradually add the dry ingredients to the wet mixture, alternating with the sour cream. Start and end with the flour mixture. Ensure everything is combined well, yielding a thick dough.

Using a cookie scoop, drop spoonfuls of dough onto the prepared baking sheet about 2 inches apart.

Combine the brown sugar and a sprinkle of cinnamon in a small bowl. Sprinkle this mixture generously over the tops of each cookie before baking.

Bake for 12-15 minutes, or until the edges are golden brown. Keep an eye on them to avoid overbaking.

Let them cool on the baking sheet for a couple of minutes before transferring them to a wire rack to cool completely.