Preheat oven to 325°F (163°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang for easy removal.
Set a heatproof bowl over simmering water. Add butter and chocolate chips, stirring until completely melted and smooth. Remove from heat and let cool slightly.
Whisk in granulated sugar and brown sugar until well combined. Add eggs one at a time, mixing thoroughly after each, then stir in vanilla.
Sift flour, cocoa powder, and salt over the chocolate mixture. Fold gently until just combined—avoid overmixing to keep bars fudgy.
Fold in chopped cherries, reserving a small handful for the top.
Spread batter into the prepared pan. Sprinkle reserved cherries on top. Bake for 28–32 minutes, until edges are set but the center still jiggles slightly.
Allow bars to cool completely in the pan. Meanwhile, whip heavy cream with powdered sugar until soft peaks form.
Use the parchment overhang to lift bars from the pan. Spread the whipped cream evenly across the top and chill for at least 1 hour before slicing into squares.
