Preheat the oven to 180°C conventional / 160°C Fan / Gas mark 4. Grease and line the bottom of two 20cm/8in sandwich tins with a circle of baking paper.
In a mixing bowl, beat the butter and sugar until light in colour and fluffy. Crack the eggs one by one and beat each one in before adding the next.
Add the vanilla extract and lime zest. Then sift the flour and baking powder into the bowl and gently fold into the mixture.
Divide the mixture evenly between the tins, using a spatula to remove all of the mixture from the bowl. Gently smooth the surface of the cakes. Place the tins on the middle shelf of the oven and bake for 25 minutes. Don’t open the door while they’re cooking.
While the cakes are cooking, add the whipping cream and rose water to a mixing bowl and whip until it forms stiff peaks.
The cakes are done when they’re golden brown and coming away from the edge of the tins. Remove them from the oven and set aside to cool in the tins for 5 minutes. You can use a thin skewer or the tip of a sharp knife to check the cakes by gently poking the centre to the bottom. It should come out clean of cake batter. Run a palette knife around the inside edge of the tin and carefully turn the cakes out onto a cooling rack. Set aside to cool completely.
To assemble, choose the sponge with the best top, then put the other cake top-down on to a serving plate. Spread with the sour cherry jam (I use the whole jar - reserve some of the jam liquid to drizzle on top of the whipped cream), then spread the whipped cream on top of the jam and drizzle the remaining jam liquid over the cream. Place the other sponge on top and dust with icing sugar and the ground pistachios.