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