Preheat your oven to 350 degrees F. Grease a bundt cake pan with shortening or non-stick cooking spray, be sure to get the tube in the middle too. Set aside.
In a small mixing bowl, whisk together the sugar and cinnamon for the filling. Add in the vanilla and whisk until combined. Set aside 1/4 cup of the filling for later.
In a large mixing bowl, beat together the butter and sugar on medium speed. Add the eggs and vanilla and mix until combined and smooth.
In a medium mixing bowl, stir together the flour, baking powder, and baking soda. Add half of the flour mixture to the wet ingredients and mix. Add the sour cream to the batter and mix again. Then add the rest of the flour to the bowl and mix until just combined.
Pour half of the batter into the prepared bundt cake pan. Sprinkle the filling all over the batter. (Keep it away from the edges to prevent sticking. )Then pour the rest of the batter into the pan, spreading into an even layer. Top the cake batter with the reserved 1/4 cup of filling.
Bake for 35-40 minutes, or until a toothpick inserted halfway between the wall and tube of the pan comes out clean.
Remove the coffee cake from the oven and let it cool on a wire rack. Once cooled, run a knife around the out edge and inner tube of the pan and then turn the coffee cake out onto a serving plate.
If you want to glaze the cake: Stir together the powdered sugar at 2 tablespoons of warm milk in a medium mixing bowl. Add a little milk at a time and then mix until the glaze has a glue-like consistency. It should be thick, but run off the spoon. (see note) Drizzle all over the bundt cake before cutting it into 12 slices.
Notes
If you don't have salted butter on hand, add 1/4 teaspoon of salt to the flour mixture.
If the glaze is too thick, it will harden and crack when you slice the cake. If it's too thin, it won't stick to the cake or it'll just soak in. You can always do a test drizzle to check the consistency. If your glaze gets too thin, add some more powdered sugar to thicken it back up.
You can also make this Sour Cream Coffee Cake in a loaf pan. The recipe is the same and will fill one 9-inch x 5.5-inch loaf pan. You'll sprinkle half of the filling mixture in the middle of the batter and then sprinkle the other half of the topping on top of the cake batter. Bake for 45-50 minutes, or until a cake tester comes out clean.