1. Preheat the oven to 180oC, and grease and line a 24cm springform tin.
2. place the butter in a large non stick frying pan over high heat. Cook, stirring for 5 minutes until melted and nutty brown in colour.
3. Transfer the brown butter to a large bowl and all the remaining ingredients.
4. Whisk until smooth but do not over mix, pour into the prepared tin and smooth the top with a spatula.
5. Bake for 1 hour 10 minutes or until cooked when tested with a skewer.
6. Allow to cool for 10 minutes in the tin before turning out onto a wire rack to cool completely.
1. Place the two chocolates in a double boiler and whisk until smooth.
2. Remove from the heat and whisk in the sour cream.
Place the cake on a cake stand or plate and spread with the ganache.