Position a rack in the center of the oven and heat the oven to 350°F. Lightly butter a 9x9x2-inch pan or other 10-cup ovenproof baking dish. Make the topping: In a food processor, pulse the flour and the oats until the oats are finely ground. Add the brown sugar, granulated sugar, cinnamon, and salt and pulse until just combined. Add the butter and pulse in short bursts until the mixture just starts to form crumbs and has a streusel-like consistency. When squeezed together with light pressure, the mixture should just clump. Add the pecans and pulse just to blend; you don’t want to chop the nuts further. Assemble and bake the crisp: In a large bowl, combine all of the filling ingredients and gently toss until well combined. Transfer the mixture to the prepared baking dish. Press down to compact slightly into an even layer. Sprinkle the topping in a thick, even layer all over the filling. Bake until the topping is golden brown, the juices are bubbling around the edges, and the apples are soft when pierced with the tip of a knife, 55 to 60 minutes. Transfer to a rack to cool for 20 to 30 minutes before serving. The crisp can be served warm or at room temperature, but it’s best served the day it’s made. Make Ahead Tips You can make and refrigerate the pecan topping topping up to 2 days ahead, or freeze for up to 2 months. Bring to room temperature before using..