Heat oven to 325 F / 163 C degrees. Spray a bundt cake pan with nonstick cooking spray. Dust lightly with all-purpose flour.
In a standing mixer beat butter on medium-high until light and fluffy, 2 to 3 minutes. Add sugar and beat until well incorporated, 1 minute more. Add mashed bananas, eggs and vanilla and blend on medium just until batter is smooth and even, 1 to 2 minutes.
In a separate bowl, whisk together flour, baking soda and salt.
Turn mixer on low speed and alternate adding a bit of the dry ingredients with the buttermilk, letting the mixer run for a few seconds between each addition. Mix on low just until everything is evenly combined.
Add first half of chocolate chips and mix on low until chips are mixed in.
Pour batter into bundt cake pan. Bake until cake is set in the middle and golden brown on top, 65 to 70 minutes.
Allow cake to cool in pan at room temperature for 20 minutes. Then invert onto a cooling rack and let cool completely.
When cake is cool heat second half of chocolate chips in the microwave in 20 second increments (stirring between each increment) until fully melted. Drizzle chocolate over cake.
Slice and serve!
Cake can be stored in the refrigerator for 3 to 4 days and will still be moist and delicious. (It keeps best without the glaze, but is fine either way)