Preheat an oven to 180c (350f). Butter the bundt cake pan with room temperature butter and flour to prevent the cake from sticking to the pan.
In a big mixing bowl, add the room temperature butter, sugar, brown sugar, vanilla extract, and kosher salt, and mix with an electric hand mixer until it's creamy.
Add the room temperature eggs, sour cream, oil, and mix until combined.
Add ½ of the flour and the baking powder, and ½ of the buttermilk, and mix until almost combined.
Add the rest of the flour and the buttermilk and mix until just combined and there are no lumps of flour visible. Dont overmix!
In a small mixing bowl, add the granulated sugar and the cinnamon and mix well until combined.
Fill the pan halfway with the cake batter, then sprinkle an even layer of cinnamon sugar on. Top the cake with the remaining cake batter, and make swirls using a knife.
Bake in a 180c (350f) oven for about an hour or until a toothpick inserted into the cake comes out clean.
Allow the cake to cool to room temperature before flipping the cake. Top the pan with a plate, flip the cake and tap the cake pan to release the cake from the pan.
Make the icing
In a medium-sized bowl, add the softened cream cheese, softened butter, powder sugar, and vanilla extract. Mix with a spoon or a tiny whisk until creamy and smooth.
Top the cake with the glaze and let it sit for a few minutes before serving. Enjoy!
Notes
Use room temperature ingredients. It is important that you use room-temperature ingredients like eggs and butter. This step ensures that your mixture mixes into a homogenous mixture and bakes perfectly. you don’t want to place cold batter into the oven.
Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.
Don’t overmix the batter, you don’t want to develop the gluten in the flour. This step ensures you have a moist cake and not a dense and dry cake.
Butter your bundt pan with butter and sprinkle flour to prevent sticking. This step helps the cake to bake evenly, and it makes sure that your cake will release easily from the pan.
Make sure that your butter is at room temperature. An hour or two before making this cake, take the butter out of the fridge and let it come to room temperature. The butter should be soft to the touch. If your butter is too cold, it will be harder to mix and there will be lumps of butter in your mixture.
Be patient! I know it’s extremely tempting to flip this cake as soon as it's ready. Allow the cake to cool to room temperature before flipping the cake. This step prevents the cake to fall apart.