Preheat oven to 350 F.

In a large mixing bowl, combine butter, oil, and sugar. Mix until smooth and well combined.

Add eggs one at a time, mixing thoroughly after each addition. Stir in red food dye, vanilla extract, and vinegar until mixed well.

In a separate medium bowl, sift together cake flour, baking soda, kosher salt, and cocoa powder. Gradually add this mixture to the wet ingredients in three batches, alternating with buttermilk, ensuring all lumps are removed by mixing well for up to 2 minutes.

Spray the mini bundt pan with non-stick cooking spray and fill each cavity 3/4 full with batter. Top each with 4-5 chocolate chips.

Bake for 15-18 minutes or until a toothpick inserted comes out clean. Let them cool in the pan for 5 minutes before inverting onto a wire rack to cool completely.