In a heavy saucepan, add milk, vanilla beans, and cassia sticks tied in a loose knot and bring to a simmer on medium heat. Concurrently, in a mixing bowl, whisk eggs and sugar together. When the milk reaches a simmer, whisk in 1 cup of the hot milk to the egg mixture. Whisk this mix back to the hot milk, reduce heat to low and constantly stir with a wooden spoon.
When mixture thickens enough to coat the back the wooden spoon and a line drawn with your finger holds it shape (about 12 to 15 minutes), immediately strain through a chinoise (fine sieve) into another bowl (a little smaller than the ice bath bowl) and place in ice bath. Stir occasionally to cool down. If there are any vanilla beans left on the pods, scrape into the anglaise. Stir to incorporate and chill sauce until ready to use.Sift the flour, salt and sugar into a food processor fitted with a blade. Add the butter and pulse until it resembles coarse meal, there should be pieces of butter. Add the ice water, 1 tablespoon at a time, pulsing the processor. Only add enough water until the dough just holds together (about 3 to 4 tablespoons). Wrap in plastic and put in the refrigerator for 30 minutes.
Vanilla Ice Cream: Freeze according to machine?s instructions.
Bittersweet Chocolate Tart: Preheat oven to 375 degrees F.
On a lightly floured surface, roll out dough to about 9-inch diameter. Use an 8-inch false bottom tart pan and carefully place dough into the pan. Work the dough into the corners and prick with a fork. Cover with foil and refrigerate for 30 minutes. Fill pan with pie weights, rice or beans and bake blind for 15 minutes. Remove foil and bake an additional 5 to 7 minutes, until the dough becomes very light tan. Pull pan out of the oven and let cool at room temperature.
For the filling, bring the cream to a simmer. Pull off of the heat and add the chocolate. When chocolate is completely melted, mix well, and let cool in the refrigerator. When chocolate mixture is cold, pull out of the refrigerator and whisk in the eggs just until incorporated. Pour into the tart shell and bake at 350 degrees for 12 to 15 minutes. It should still tremble in the center when lightly shaken. Let tart cool on a rack before demolding. Garnish with powdered sugar and cocoa powder.
On a large plate, garnish the rim of the plate with powdered sugar and cocoa powder. Ladle a small pool of creme anglaise. Place a slice of the tart off of the side and place 1 scoop of ice cream next to it. For the ultimate, make individual tarts.