Just look at this thing of beauty.
Adapted it slightly from the Rose Bakery recipe:

Sweet pasty (make your own or buy one)
3 egg yolks
2 eggs, 1 blended for basting the pastry (to then be used in the tart)
100g caster sugar
1 tsp natural vanilla extract,
grated zest of 3 oranges, 500g ricotta cheese
roughly 180g grated dark chocolate (70% or more)
1 tablespoon plain flour

Preheat oven to 180 deg C

Put pastry in 28cm (roughly) tart tin, chill for 30 mins, then blind bake for 10 minutes.
Remove the weights from the pasty case, and baste it thoroughly with the mixed egg. Bake another 10 minutes.
Remove and let cool slightly.

Beat the egg yolks and eggs with the sugar until light and fluffy.
Add the vanilla, orange zest, ricotta, and mix well
Fold in the chocolate, and finally the flour.
Pour into the tart case and bake for about 25-30 mins until the filling has just set.
Remove from the oven & serve at room temp (or a bit warmer).