Apple and mascarpone torta

1.Preheat oven to 170C. Beat butter, caster sugar and lemon rind in an electric mixer until pale and fluffy (2-3 minutes), scrape down sides of bowl and beat in egg. Sift in flours, fold to combine, stir in milk and mascarpone, spoon into a 23cm-diameter springform tin, buttered and dusted with flour, smooth top.

2.For mascarpone filling, whisk ingredients in a bowl until smooth, then spoon over cake batter and smooth top.

3.For apple topping, toss apple slices in lemon juice and arrange, overlapping slightly, on top of mascarpone mix. Brush with melted butter, scatter with demerara sugar, bake until golden and risen (50 minutes-1 hour). Cool in tin for 20 minutes, then run a sharp knife around sides of tin to loosen cake, remove sides of tin, cool cake to room temperature and dust with icing sugar. Torta will keep stored in an airtight container for 2 days.