Preheat oven to 160 degrees celsius (fan-forced). Grease and line the base and sides of a 23cm springform tin well with baking paper.
Melt the butter and chocolate together in the Thermomix for 3 minutes, 50 degrees, Speed 2. Set aside to cool.
Wash and dry the Thermomix bowl. Insert the butterfly and add the caster sugar and eggs. Beat for 6 minutes, Speed 4.
Reduce to Speed 3 and with the butterfly still turning, slowly add the cooled chocolate mixture, plain flour, ground almonds and salt. Mix on Speed 3 until combined (you might need to scrape down the sides of the bowl partway through).
Bake for 30 minutes or until just set in the middle (the top will form a lovely crust). Allow to cool in the tin for 15 minutes before removing to a serving plate.
Serve dusted with cocoa powder, fresh raspberries and ice-cream (optional).