Melt chocolate and butter in a saucepan, then whisk in both sugars.
Add eggs and vanilla extract, then fold in sifted dry ingredients.
Gently fold in raspberries; the batter will be thick.
Spread batter into prepared pan, top with berries and optional jam, swirl gently.
Bake until edges are set and center slightly jiggles, about 35 minutes.
Let brownies cool fully on a rack before cutting.
Notes
For a richer flavor, use high-quality chocolate. Feel free to adjust the amount of raspberries or jam to suit your taste. Store in an airtight container for up to 3 days.