Lemon slab cake
You will need one 20cm x 30cm (8in x 12in) Swiss-roll tin. Preheat the oven to 180°C, 350°F, Gas 4. Line the base and sides of the tin with parchment paper.
Melt the butter on a low heat, then pour it into a mixing bowl. Add in the sugar and whisk to mix with the melted butter, then mix in the eggs, the creme fraiche, the lemon zest and the lemon juice. Sift in the flour and the baking powder and fold them into the mixture. Tip the cake mixture into the prepared tin. Place the tin in the preheated oven and bake the cake for 25-30 minutes or until a skewer inserted into the centre comes out clean. Allow the cake to cool completely before icing it.
To make the icing, put the sifted icing sugar into a bowl and add the lemon juice gradually - you may not need it all. If it's still too stiff when you've added it all, then add a tiny bit of water to bring the icing to a spreadable consistency.
Spread the icing over the top of the cooked cake, and allow it to dry - this should take about 20 minutes - then cut it into slices to serve.