dina, i couldn't find a good tart recipe for frutti di bosco, but here's what you can do.
a frutti di bosco tart is essentially a tart pastry, filled with zabaglione (custard), and topped with fresh berries, and then drizzled with a simple syrup wash.
ingredients:
fresh raspberries, blueberries, blackberries, strawberries (sliced), etc. whatever fresh berries are available
tart pastries or shells
melted sugar mixed with a little water to thin
for the zabaglione:
4 egg yolks
i tbsp marsala wine or sweet wine
1/4 cup sugar
2 tbsps warm water
2 tbsps mascarpone cheese
combine eggs, wine, water and sugar in a bowl over a bain marie (simmering water bath), and whip for about 5 minutes. fold in the mascarpone cheese to incorporate.
fill the tart shells with the zabaglione, gently top with mixed fresh berries, brush or drizzle tops with the sugar syrup until covered, chill to let it set up.