Preheat oven to 180°C, fan 160°C, gas 4. Grease and line 2 x 20cm sandwich tins with baking paper.
In a large bowl, beat all sponge ingredients together with a wooden spoon until the mixture is light and smooth.
Divide the mixture between the 2 tins, level the top and bake for 20 minutes or until a skewer comes out clean. Leave to cool in the tins for 5 minutes then turn out onto a cooling rack.
To make the filling, beat the icing sugar and butter together with an electric whisk until pale and fluffy. Beat in the 150g melted white chocolate cake covering.
Starting at a slow speed, beat 100g of the chopped strawberries into the butter mixture, with the vanilla paste. When all the ingredients are mixed together, increase the speed until the mixture is smooth, fluffy and a gorgeous pink colour.
Combine the remaining 175g chopped strawberries with the mint. Put one of the sponges onto a cake stand or plate, securing it with a little filling underneath.
Using a piping bag, pipe large bulbs of the mixture around the edge of the cake, then cover the middle with the strawberries and mint.
Top with the second sponge and pipe the rest of the mixture in bulbs around the edge. Chill the cake for up to 1 hour to set.
To decorate, dip three large strawberries into the 75g melted white chocolate cake covering and leave to set. Spoon the dark chocolate cake covering into a piping bag and pipe over the white chocolate covered strawberries.
Put these in the centre of the cake with the other berries. Dust with icing sugar and gold lustre to finish.