Raspberry sponge slices

For the sponge:

200g soft butter

190g golden caster sugar

4 eggs

the zest of an orange

2 tsp vanilla extract

200g self-raising flour, sieved

To glaze:

35g golden caster sugar

25mls Grand Marnier liqueur – or similar

For the filling:

250g mascarpone cheese

15g icing sugar

250ml cream, whipped to stiff peaks

200g ripe raspberries