For the pastry cream: In a small saucepan, bring the milk and vanilla bean pod and seeds to a boil over medium heat. Once it comes to a boil, cover the pan, remove it from the heat, and let steep for 15 minutes.
In a bowl, whisk the egg yolks, sugar and cornstarch together until very thick. Slowly drizzle one-third of the hot milk into the yolks, whisking constantly. Remove the vanilla bean pod. Return the yolk mixture to the saucepan. Place over medium heat and cook, whisking continually, until the mixture comes to a boil. Continue whisking while the mixture boils for 1 to 2 minutes.
Remove from the heat. Whisk slowly until the mixture cools a bit, 3 to 4 minutes. Whisk in the butter 1 tablespoon at a time.
The pastry cream needs to be chilled before using. One method is to cover the surface of the cream with a sheet of buttered parchment, or butter wrappers, and refrigerate it until it is very cold. The other method, which I prefer, is quicker: Set the bowl of pastry cream in a larger bowl filled with lots of ice and some cold water and allow it to sit until very cold. (Think of chilling a bottle of wine or champagne-you need some water to ensure even cooling.) If you choose this method, stir the cream occasionally for even cooling. The pastry cream can be made up to 3 days in advance and refrigerated.
For the crumble topping: Preheat the oven to 350 degrees F. Place the pecans on a baking sheet and bake until toasted, 10 to 12 minutes. Remove and let cool. Coarsely chop 1/4 cup of the pecans.
Put the remaining 3/4 cup pecans in a food processor along with 1/2 cup of the cake flour. (The flour will help keep the nuts from turning into pecan butter.) Pulse the pecans until they're very finely chopped. Add the rest of the flour, the confectioners' sugar, turbinado sugar, salt and baking powder. Pulse until mixed, 3 to 4 times.
With the machine running, add the melted butter and vanilla. Pulse until large clumps form. Transfer the mixture to a bowl and stir in the reserved 1/4 cup chopped pecans. Refrigerate until chilled. The topping can be made several days in advance and can also be frozen for up to 1 month.
To bake the betties, heat the oven to 350 degrees F. Have ready eight 6-ounce ramekins or baking dishes.
Divide the chilled pastry cream evenly among the ramekins. The cream should fill just under one-third of the ramekin. I like piping the cream into the ramekins, but using a spoon old-school works just as well.
Evenly portion the berries on top of the pastry cream. Remove the crumble from the refrigerator. Break off clumps about 1/2 to 3/4 inch in diameter, keeping the clumps about the same size, and divide them evenly among the ramekins.
Arrange the ramekins on a baking sheet and place in the oven. Bake until the berries start to bubble and the topping turns golden brown, 10 to 12 minutes.
Remove from the oven, let cool for 10 to 15 minutes, and serve dusted with confectioners' sugar. You can also serve the betties topped with ice cream, whipped cream or creme fraiche, or you can pour a little warm heavy cream into each betty.