1. Make crust: Pulse flour, powdered sugar, and salt in a food processor to blend. Add butter and pulse a few times until dough looks like cornmeal. Slit vanilla bean and carefully scrape out seeds with a spoon; add to dough. Drizzle in egg mixture and pulse until dough comes together.
2. Flatten dough into a disc and chill, wrapped in plastic wrap, at least 1 hour and up to 2 days.
3. Roll dough on a lightly floured surface with a lightly floured rolling pin into a 10 1/2-in. circle. Ease dough into a 9-in. tart pan and, using your thumb, press into sides and bottom corner; fold edges over to help form rim. Line shell with parchment paper and fill completely with dried beans or pie weights. Chill at least 1 hour and up to 1 day.
4. Preheat oven to 325°. Bake shell 15 to 25 minutes, or until lightly golden on the edge and set on the bottom (lift up parchment to check). Carefully remove parchment and weights and bake shell until pale golden, 5 to 10 minutes more. Transfer tart shell to a rack, and lower oven temperature to 250°.
5. Make filling: Put chocolate in a medium heatproof bowl. Heat cream and half-and-half in a medium saucepan over medium heat until simmering, then pour over chocolate. Let sit a few minutes, then stir gently until smooth.
6. Break egg into a separate medium bowl, then pour into chocolate mixture, whisking constantly until incorporated (keep whisk in contact with bottom of bowl so as not to whip in air bubbles). Pour mixture into the tart shell and bake until just set (no longer jiggles), 25 to 35 minutes. Let cool completely.
7. Make topping: Warm cherries in a saucepan over low heat with granulated sugar to taste until sugar melts. Whip cream with 2 tbsp. sugar and almond extract until soft peaks form.
8. Cut tart into slices and serve each with a few cherries and a dollop of cream on top.
Make ahead: Up to 2 days, chilled (bring to room temperature before serving).
Note: Nutritional analysis is per slice, with cherries and cream.