Preheat the oven to 180℃ (170℃ fan)/400°F/gas mark 4. Grease and line the base of 3 x 23 cm (9in) shallow cake tins.
Beat the butter and caster sugar together until very pale and fluffy. Then beat in the eggs one at a time adding 1 tbsp of flour with each of the last two eggs to prevent them from curdling.
Sift the remaining flour and baking powder into the bowl. Add the pistachios and the juice and zest of two limes. then carefully fold in until the mixture is well combined.
Divide equally between the three tins and bake for 30 minutes or until springy to the touch.
Allow to cool in the tins for a few minutes then turn out onto a wire rack and allow to cool completely.
To make the butter cream
Beat the butter until pale, then add the icing sugar a third at a time and beat until combined. Add the lime juice and beat until very fluffy.
Spread about one third of the butter cream over one of the sponge layers. Place the next one on top and repeat with another third of the icing and the third sponge.
Use the remaining butter cream to coat the top and sides of the cake. Pile some berries on top of the cake and sprinkle with a few pistachio nuts. Dust with icing sugar and serve
Place a shallow roasting tin in the base of the oven and fill with 2cm (1in) hot water before baking the cakes. This helps to keep the cakes moist while they cook.
If you do not have three cake tins or enough space in the oven to cook three at once, the mixture can stand while one batch cooks. Remove the cake from the tin, reline and grease the cake tin and bake the remaining cake layer as quickly as possible so that the mixture does not sit for too long.
Nutrition calculations does not include the fruit and nuts on top.