Preheat oven to 350°F. Generously butter and flour a large bundt pan or spray with baker's spray.
In a large bowl, beat the butter and sugar together until light and fluffy, about 2-3 minutes.
2 cups granulated sugar, 1 cup salted butter
Add the vanilla and eggs, making sure to mix well and scrape the sides and bottom of the bowl.
1 1/2 teaspoons pure vanilla extract, 3 large large eggs
In a separate bowl, whisk together the flour, cocoa powder, baking soda, salt, and chocolate pudding. Add the dry ingredients alternately with the buttermilk, mixing between each addition until combined.
2 1/2 cups cake flour, 1 cup natural unsweetened cocoa powder, 2 teaspoons baking soda, 1/2 teaspoon salt, 1/2 cup instant chocolate pudding mix, 2 1/4 cups buttermilk
Stir in the chocolate chips, then transfer the thick cake batter to the prepared bundt pan.
1 cup semi-sweet chocolate chips
Bake for 50-60 minutes until a skewer inserted into the center of the cake comes out clean with just a few crumbs.
Cool for 15 minutes, then turn out onto a wire rack to cool completely before icing.