Preheat the oven to 350°F (175°C). Line an 8×8-inch pan with parchment paper, leaving an overhang for easy lifting.
In a heatproof bowl, melt the butter and chocolate together until smooth. Stir in the sugars while warm.
Whisk in eggs and vanilla until the mixture becomes thick and shiny.
Sift in flour, cocoa powder, and salt, then fold gently with a spatula until just combined. Do not overmix.
Fold in half of the raspberries and any optional add-ins like chocolate chips or nuts.
Spread the batter into the prepared pan and press the remaining raspberries gently on top.
Bake for 25–30 minutes, or until a toothpick comes out with a few moist crumbs.
Cool completely in the pan before slicing into squares for clean edges.