Preheat the oven to 180°C and line or grease a round baking form, about 20 cm diameter.
Melt the dark chocolate gently over a water bath, then remove from the heat and stir until smooth.
Beat the eggs, egg yolks and brown sugar until light and slightly foamy.
Blend or mash the avocado until completely smooth, then stir it into the egg mixture.
Add the melted chocolate, walnuts, cocoa powder, citrus zest and salt. Mix gently until smooth.
Pour the batter into the prepared round form and press the frozen raspberries lightly into the surface.
Bake for about 22–28 minutes, depending on the depth of the form. Insert a wooden skewer or toothpick into the center — if it comes out mostly clean with just a few moist crumbs, the brownie cake is ready.
Let it cool fully in the form before slicing into cake-style pieces.