Preheat the oven to 350°F (177°C). Line a 12-count muffin pan with cupcake liners. Line a second pan with 2 liners—this recipe makes about 14 cupcakes. Set aside. In a large bowl, whisk the cocoa powder, flour, baking soda, baking powder, and salt together until thoroughly combined. Set aside. In a medium bowl, whisk the eggs, sugar, brown sugar, oil, and vanilla together until completely smooth. Pour half of the wet ingredients into the dry ingredients. Then half of the buttermilk. Gently stir—about 5 stirs. Repeat with the remaining wet ingredients and buttermilk. Stir until *just* combined; do not overmix. The batter won’t be very thick. Pour/spoon the batter into the liners—fill only halfway to avoid spilling over the sides. Bake in batches for 18-19 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely before frosting. For around 30 mini cupcakes, bake for about 11-13 minutes, same oven temperature. Beat softened butter on medium speed for about 3-4 minutes until completely smooth and creamy. Add the confectioners’ sugar, cream, vanilla extract, and salt with the mixer running. Increase to high speed and beat for 1 minute. Add the raspberry preserves and beat until thick and creamy, about 2 full minutes. Add more confectioners’ sugar if frosting is too thin, is separating (due to the fruity jam) or looks too wet. And then add more salt to offset added sweetness. Frost cooled cupcakes however you’d like. I simply used a small frosting knife to frost the cupcakes. Top with fresh raspberries if desired. Leftover cupcakes keep well covered tightly at room temperature or in the refrigerator for 3 days. I recommend a cupcake carrier for storing and transporting decorated cupcakes.