Preheat oven to 350°F (175°C). Grease a 9x9-inch square baking pan or line with parchment.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
In a large bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, mixing well.
Mix in sour cream and vanilla until smooth.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
In a small bowl, mix brown sugar and cinnamon.
Spread half of the batter into the prepared pan. Sprinkle with half of the cinnamon-sugar mixture and half of the chocolate chips.
Spread remaining batter on top. Sprinkle with the rest of the cinnamon sugar and chocolate chips.
Bake for 38–42 minutes, or until a toothpick inserted in the center comes out clean.
Let cool for 30 minutes before slicing.