Preheat your oven to 350°F (175°C) and generously grease and flour a bundt pan.

In a medium bowl, whisk together the flour, baking powder, and salt until well combined.

In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3-5 minutes.

Add the eggs one at a time, mixing thoroughly after each addition, then blend in the sour cream and vanilla extract until smooth.

Gradually add the dry ingredients to the wet mixture, alternating with the milk, mixing until just combined. Be careful not to over-mix.

In a separate small bowl, stir together the brown sugar and cinnamon.

Pour half of the batter into the prepared bundt pan. Sprinkle half of the cinnamon-sugar mixture over the batter, then layer the remaining batter on top.

Finish by sprinkling the rest of the cinnamon-sugar mixture over the last layer of batter.

Use a knife to gently swirl the batter to mix the cinnamon-sugar throughout.

Bake in the preheated oven for 50 to 60 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cake to cool in the pan for about 15 minutes before inverting it onto a wire rack to cool completely.

For the glaze, whisk together powdered sugar, 2-3 tablespoons of milk, and vanilla extract until smooth.

Drizzle over the cooled cake before serving.