Heat oven to 325F. Line an 8-inch square baking pan with parchment, leaving a 2-inch overhang on two sides. Lightly butter the parchment.

Combine butter and bittersweet chocolate in a medium saucepan over medium-low heat. Stir constantly until just melted and smooth, about 4 minutes. Remove from heat and let cool slightly, 5 minutes. The mixture should feel warm, not hot, to the touch.

Whisk both sugars into the warm chocolate mixture until glossy and combined. Add eggs one at a time, whisking vigorously after each until fully incorporated. Stir in vanilla. The batter should look thick and pull away slightly from the sides of the pan.

Sprinkle flour, cocoa powder, and salt over the surface. Use a wooden spoon to fold until just combined with no streaks of flour remaining. Do not overmix. The batter will be thick and fudgy.

Gently fold in dried and fresh cherries, distributing evenly without crushing the fresh ones. Scrape batter into the prepared pan and smooth the top with an offset spatula.

Bake until the top is set and cracked, and a toothpick inserted in the center comes out with moist crumbs attached, 32 to 36 minutes. The brownies will look slightly underdone in the very center. Do not overbake.

Cool completely in the pan on a wire rack, at least 2 hours. Use the parchment overhang to lift out, then cut into 16 squares with a sharp knife, wiping clean between cuts.