Preheat the oven to 350 degrees. In a large mixing bowl, beat the egg whites with an electric mixer on low speed until foamy. Add the cream of tartar and mix on medium high speed until soft peaks form.
Gradually add ½ cup of the sugar to the egg whites and beat until stiff peaks form. Set aside.
In another large mixing bowl, whisk together the remaining sugar, flour, baking powder, baking soda, and salt. Using a hand mixer on medium speed, mix in the buttermilk, oil, vanilla, and 1 heaping spoonful of the egg whites.
Fold the remaining egg whites and chocolate chips into the cake batter.
Transfer the batter to the prepared bundt pan and smooth top of the batter with the backside of a spoon.
Bake for 40 minutes, or until a toothpick inserted into the center comes out clean. Remove the bundt cake from the oven and cool for 10 minutes on a wire rack. Invert onto a cooling rack and cool completely.
Once cool, add ⅓ cup of mini chocolate chips and 2 tablespoons of milk to a small microwaveable bowl, Microwave for 40 seconds (add more time if needed). Stir until smooth.