400g plain flour
2 tsp baking soda
300ml sunflower oil
100ml greek yogurt
100ml crème fraîche
3 tsp vanilla extract
4 tsp grated lemon zest
350g golden caster sugar
500g mashed banana
For the Frosting*: (optional)
350g dark chocolate (70% cocoa solids), broken into pieces
400ml sour cream
*in my case, I decided to frost only the top of the cake, therefore halving the quantities.
Preheat the oven to 180 C/350 F. Grease and line a 23cm cake tin about 6-7cm in height/depth.
Sift the flour and baking soda into a large bowl and stir together. Add the oil and beat well until the mixture is pale and creamy.
In a separate bowl, mix the yogurt, crème fraîche, vanilla and lemon zest together and then beat into the flour mixture. Gradually add the sugar and then the eggs, one at a time, beating well after each addition. Add the mashed banana and mix until everything is combined.
Pour the batter into the prepared tin, making sure it is evenly distributed, then bake in the oven for 2 hours until a skewer inserted in the center comes out clean. (You may need to place a sheet over the top after an hour or so to keep the cake from browning too much.)
Allow the cake to cool in its tin for 10 minutes, then turn out onto a wire rack to cool completely.
Without frosting, the cake can be served while still a little warm, but otherwise, wait until it has completely cooled to frost it. For the frosting, melt the chocolate together with the sour cream, beating continually until you have a smooth consistency. Then use a palette knife to cover the top and sides of the cake with the frosting. Allow to set a little before serving.