Preheat the oven to 180℃ (160℃ fan)/350°F/gas mark 4. Grease and line the base of two 20cm/8in sandwich cake tins.
Place the pistachios in a food processor with the flour and blitz together until the nuts are very finely chopped.
Add the remaining ingredients for the cake and blitz again until the all ingredients are well blended. Divide equally between the cake tins and level the top. Bake in the oven for 30 minutes until springy to the touch.
Allow to cool in the tins for 5 minutes then turn out onto a wire rack and allow to cool completely.
Once the cake is cool, sandwich together with the lemon curd and place on a serving plate.
Beat the butter and icing sugar and lemon zest and juice until very light and fluffy. Then beat in the mascarpone cheese. Spread over the cake and decorate with the crystalised flowers.
Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)