Place the flour, granulated sugar, brown sugar, cinnamon, and salt in the bowl of a food processor fitted with a steel blade and give it a few pulses to mix.
Add the butter and pulse 5 to 7 times or until the mixture resembles small peas.
Transfer the mixture to a bowl. Stir in the oats with a spoon until mixture is crumbly. Chill until ready to use.
Prepare the Cobbler:
Melt the butter in a 13 x 9-inch baking dish while the oven preheats.
Combine the apples and brown sugar, tossing to coat. Spoon into the baking dish and bake for 15 minutes or until the apples begin to soften and release juices.
Meanwhile, whisk together the flour, sugar, baking powder and cinnamon in a large bowl. Add the milk, buttermilk, and vanilla and whisk until smooth.
When the apples are ready, remove the baking dish from the oven and pour the batter over the apples. Sprinkle with crumb topping.
Bake at 375°F for 1 hour to 1 hour and 10 minutes or until a wooden pick inserted in the center comes out clean. Let stand 15 minutes before serving.
Serve warm with whipped cream or vanilla ice cream.
Notes
This recipe for apple crisp can easily be made gluten free. Use a 1-to-1 gluten free flour replacement and gluten free oats.