01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Toss pitted and halved cherries with 1 tablespoon sugar and 1 teaspoon vanilla extract. Spread on prepared baking sheet and roast for 12-15 minutes until juicy and slightly caramelized. Allow to cool.
03 - Reduce oven temperature to 350°F. Grease an 8-inch square baking pan with butter and line with parchment paper, leaving overhang for easy removal.
04 - Set a heatproof bowl over a saucepan of simmering water. Melt butter and chopped chocolate together, stirring constantly until smooth. Remove from heat and cool slightly.
05 - Whisk granulated sugar and brown sugar into the chocolate mixture. Add eggs one at a time, whisking well after each addition. Stir in vanilla and salt.
06 - Sift flour and cocoa powder into the batter. Gently fold until just combined, being careful not to overmix.
07 - Fold most of the roasted cherries into the batter, reserving a few pieces for the topping.
08 - Pour batter into prepared pan and smooth top. Scatter reserved cherries over surface. Bake for 25-28 minutes until a toothpick inserted in center comes out with moist crumbs.
09 - Cool completely in pan before lifting out using parchment overhang. Cut into squares and serve.