Preheat your oven to 350°F (175°C). In a saucepan over medium heat, melt the butter. Stir in granulated sugar and brown sugar until the mixture bubbles and caramelizes, about 3-5 minutes. Add the drained tart cherries and vanilla extract, stirring gently for a minute before pouring into a prepared cake pan.

In a large mixing bowl, sift together flour, cocoa powder, baking powder, baking soda, and salt. In another bowl, whisk together eggs, buttermilk, vegetable oil, and vanilla until smooth. Gradually mix wet into dry, stirring until just combined, then add boiling water to loosen the batter.

Pour the cake batter over the cherry mixture in the pan. Smooth the surface to ensure the cherries are covered. The batter should flow into the nooks created by the cherries.

Bake for 35-40 minutes until a toothpick inserted in the center comes out clean or with a few moist crumbs. The edges should pull away slightly from the pan.

Let the cake cool in the pan for about 10 minutes. Run a knife around the edges to loosen, then invert onto a serving plate to reveal the caramelized cherries.