Preheat oven to 325°F Lightly coat or spray a 9- or 9 1/2-inch springform pan with oil.
Place 3/4 cup flour and 1/4 cup sugar in a food processor. Pulse to mix. Add butter. Pulse until small crumbs form. Turn into pan. Press firmly and evenly over bottom. (Don't worry about cleaning processor.)
Bake crust in centre of preheated oven until lightly golden around edge, 15 to 20 minutes. Remove pan and reduce heat to 300F
Finely grate peel from orange. Cut cream cheese into chunks.
Place in a food processor with ricotta and vanilla. Whirl until smooth, occasionally scraping down side of bowl.
Add 1 cup sugar and whirl to mix. Add eggs, one at a time, whirling after each addition. Then add 3 tbsp flour and orange zest. Whirl just until evenly mixed.
Scrape filling into a large bowl. Stir in chocolate, candied fruit mix and pistachios.
Pour filling over warm base.
Lay a piece of foil loosely overtop. Don't seal.
Bake in centre of 300F oven until centre is slightly jiggly, 2 hours.
Remove to a rack. Run a knife around outside edge of cake, but don't remove from pan. Cool in pan, then refrigerate at least 3 hours or cover and refrigerate up to 3 days or freeze up to 2 months.
If centre cracks, cover with orange slices or whipped cream and chopped pistachios, if you wish!
Hint: if you cannot find the mixed chopped candied fruits and peel use diced candied cherries and pineapple.