For the sponges:
1 Make the roasted white chocolate by preheating the oven to 120 degrees, or 100 degrees if using a fan oven.

2 Place the white chocolate onto a baking tray and roast in the oven for about an hour, stirring every 15 minutes or so. The chocolate will become chalky at first, continue stirring and baking until the chocolate becomes melted and golden brown in colour. Remove from the oven, scrape into a bowl and set aside to cool slightly while preparing the remaining ingredients.

3 Increase the oven temperature to 180 degrees, or 160 degrees fan. Grease and line 3 x 20cm cake tins with parchment paper.

4 Cream the butter and sugar together in a large bowl until pale and creamy. Add the eggs one by one, beating in each one until fully combined, before adding the next.

5 Add the lime zest then sift in the flour and baking powder and mix until just combined. Pour in the cooled roasted white chocolate and fold it through.

6 Divide the mixture between the tins and bake in the preheated oven for 20-25 minutes, until a skewer inserted into the centre comes out clean.

7 Remove the sponges from the oven and leave to cool for five minutes in the tin before turning out onto a wire rack to cool completely.

For the frosting:
1 Beat the butter in a large bowl until very soft and smooth. Add the icing sugar and beat well, about 3-5 minutes, until very pale.

2 Add the cream cheese and vanilla, mixing again slowly until just combined, then continue to beat for another few minutes until thick and fluffy.

To assemble:
1 Place the first sponge on a serving plate. Spread half of the frosting between the sponge layers then cover the whole cake with the remaining frosting.

2 Grate some white chocolate on top of the cake and finish with a grating of fresh lime zest to serve.