Heat the oven to 350°F with a rack in the lower third of the oven (preferably with a baking steel or stone on it). Place the cooled par-baked crust on a baking sheet and arrange the fruit in an even layer inside it.
In a medium bowl, rub the vanilla bean seeds into the sugar. Add the flour and whisk to combine. Add the milk, cream, and eggs, and whisk well to combine. Add the salt and cinnamon.
Gently pour the custard into the prepared pie crust. Bake until the pie appears set at the edges but is still slightly jiggly in the center, 45 to 55 minutes. Let cool for 15 minutes, then dust with confectioners’ sugar and serve warm (or let cool to room temperature and refrigerate until ready to serve—dust with sugar just before serving).