You will need 4 thick slices of panettone. Each should weigh about 60g.
Make a light lemon syrup by squeezing enough lemons to give 100ml of juice. This will probably be about 3, depending on their size and ripeness. Put the juice in a small saucepan with 4 tbsp of caster sugar and bring to the boil. Remove from the heat as soon as the sugar has melted and cool before use.
Put 500g of mascarpone in a mixing bowl and stir in 350g of lemon or passion fruit curd. (You can use orange curd too but it lacks the dazzling sharpness of the other two.)
Place a slice of panettone in the bottom of a deep cake tin, then sprinkle it with some of the lemon syrup. Place one quarter of the mascarpone frosting over the panettone, smoothing it level, then place a second slice on top. Sprinkle that, too, with some of the syrup, then another layer of mascarpone. Keep going until all the slices of cake are used up, finishing off with mascarpone.
Cover loosely and refrigerate for a good half-hour before slicing and serving. Serves 6
To chill the lemon syrup quickly, pour into a bowl and place in a deep bowl of ice cubes. The syrup will be cool enough to use in 10 minutes or so.
You could use slices of open-textured sponge cake if you prefer.
Should you wish, you could assemble your cake as a sort of trifle instead, tearing the panettone into small pieces, soaking them with the lemon syrup, then spooning over the lemon curd and mascarpone topping followed by a layer of whipped cream.
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