Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

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

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

Gradually add the dry ingredients to the wet mixture, alternating with the sour cream, and mix until just combined.

In a small bowl, mix together the brown sugar and ground cinnamon.

Scoop about 1 tablespoon of cookie dough and flatten it slightly. Sprinkle a teaspoon of the brown sugar mixture in the center, and fold the dough over to seal it. Roll it into a ball and place it on the prepared baking sheet. Repeat with the remaining dough.

If using, sprinkle chopped nuts on top of each cookie before baking.

Bake for 10-12 minutes or until the edges are lightly golden.

While the cookies are baking, prepare the glaze by mixing the powdered sugar with milk until smooth. Adjust the consistency by adding more milk if necessary.

Once the cookies are done, let them cool on the baking sheet for a few minutes before transferring them to a wire rack. Drizzle the glaze over the cooled cookies.