Preheat oven to 350 degrees and line 24 cupcake cups with liners.
Place cake mix, brownie mix, oil, sour cream, buttermilk, eggs and pumpking into stand mixer. Beat until well combined, about 1-2 minutes. Scoop batter into lined cups 3/4 full. Bake for 22-27 minutes, until baked through. Remove and let cool completely.
While cupcakes are cooling, place butter into stand mixer and beat until creamy. Slowly add powdered sugar until you’ve got a nice consistency. Stir in vanilla bean seeds and milk until smooth. Frost over cupcakes and top with mini chocolate chips.