To make the hot chocolate, place all ingredients into the Thermomix bowl and combine 20 sec/speed 4. Warm 5 min/70°C/speed 3.
To make the meringue, place egg white into a very clean Thermomix bowl. Whip 4 min/Butterfly/37°C/speed 3. Slowly add sugar 4 min/Butterfly/speed 3.
Pour hot chocolate into mugs and top with meringue. Dust with cocoa.