Preheat oven to 350°F (175°C). Greased a 10-12 cup bundt pan heavily with shortening and dust with cocoa powder. In a bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt.

In a stand mixer, beat the butter, oil, granulated sugar, and brown sugar on medium-high speed for 3-4 minutes until fluffy. Add eggs one at a time, mixing well after each. Stir in vanilla extract.

Alternate adding the dry ingredients and sour cream to the wet mixture on low speed in three and two batches respectively. Do not overmix. Toss the dark chocolate chips in 1 tbsp of flour, then fold them into the thick batter.

Pour batter into the prepared pan, smooth the top, and tap to release air bubbles. Bake for 45 to 55 minutes, until a wooden skewer comes out with moist, fudgy crumbs.

Cool the cake in the pan on a wire rack for exactly 15 minutes. Invert the pan onto the wire rack to release the cake. Let cool completely to room temperature.

Whisk sifted powdered sugar, 3 tbsp heavy cream, and vanilla extract until smooth and thick. Add 1 more tbsp cream if it is too stiff to drip.

Drizzle the thick white icing over the cooled bundt cake, allowing it to drip down the fluted sides. Immediately sprinkle mini chocolate chips over the wet icing. Let set for 20 minutes before slicing.