Preheat your oven to 325°F (163°C) and grease a bundt pan well to ensure the cake comes out easily.
In a medium bowl, whisk together the flour, baking powder, and salt. In a larger bowl, beat the softened butter and granulated sugar until fluffy. Then, add the eggs one at a time, mixing well after each. Add in the vanilla extract and sour cream next. Gradually add the dry ingredients until everything is just combined.
For the cinnamon swirl filling, mix the brown sugar, ground cinnamon, and melted butter in a small bowl. Pour half of your batter into the bundt pan, add the swirl filling, and then gently swirl it with a knife. Pour the remaining batter over the top.
Bake for 60–70 minutes, or until a toothpick comes out clean from the center. Let the cake cool in the pan for about 15 minutes, then transfer it to a wire rack to cool completely.
To make the glaze, beat the softened cream cheese until smooth. Then mix in the powdered sugar, cinnamon, vanilla, and enough milk to reach your desired thickness. Drizzle this over your cooled cake. If you want, dust it with some cinnamon-sugar for a little sparkle. Serve it warm with a scoop of vanilla ice cream for extra deliciousness!