Preheat oven to 350F. Lightly grease a 9-in bundt cake pan. Set aside.
In a large bowl, whisk butter, sugar, eggs, sour cream, buttermilk, and vanilla until smooth. Add flour, baking powder, baking soda, salt, and cinnamon and gently fold until a smooth batter forms. Fold in chocolate chips.
Scrape batter into prepared pan and smooth top. Bake coffee cake at 350F 40-45 minutes or until a toothpick inserted in middle comes out with moist (but not gooey) crumbs sticking to it. Cool cake in pan 20 minutes, then run a knife around edges and invert onto a serving plate.
Make the glaze: In a small bowl, whisk powdered sugar, vanilla, and just enough milk to achieve a drizzling consistency.
Drizzle glaze over cooled coffee cake and let stand 5 minutes before serving. Slice coffee cake and enjoy!