6 tablespoons (85 g) cold unsalted butter, cut into 1/2 inch dice
5 medium (794 g/ 1 3/4 pounds) nectarines, or peaches
2 cups frozen blueberries
1/2 cup vanilla sugar
3 tablespoons cold unsalted butter, cut into 1/8 inch dice
1 teaspoon freshly squeezed lemon juice
1 vanilla bean
1 tablespoon all-purpose flour
1 tablespoon cornstarch
Preheat the oven to 350 degrees. To make the crisp topping, combine the oats, brown sugar, cinnamon, toasted pecans, and flour in a bowl. Add the diced butter and blend with a pastry blender or the tips of your fingers until crumbly. Set aside.
Cut the nectarines in half, remove the pits, and then slice them 1/4 inch thick. You should have about 4 cups sliced nectarines. Put the nectarines, blueberries, sugar, butter, and lemon juice in a large bowl. Split the vanilla bean lengthwise and use a paring knife to scrape out the seeds. Add the vanilla bean scrapings to the bowl. Sift the flour and the cornstarch into the bowl and gently combine all the ingredients using a rubber spatula.
You can either put the whole crisp in one 9-inch pie pan or multiple ramekins. Evenly distribute the crumble all over the top. Put the pie plate or ramekins on a baking sheet to catch any drips and place it in the oven. Bake until the fruit is cooked and bubbling and the topping is golden, 50 to 55 minutes, rotating the pan halfway through the baking time.
Remove the pan from the oven and cool briefly on a wire rack. Serve while the crisp is still warm.