Directions

• Preheat oven to 400 degrees (F). Prepare streusel topping by combining brown sugar, flour, oats, cinnamon, and salt in a medium bowl (mixing the ingredients first by hand prevents the oats from getting chopped up too finely in the food processor). Transfer ingredients to your food processor. Scatter in butter, then pulse 10 times. Process continually for 10-15 seconds, only until no visible lumps of butter appear. Transfer mix back into medium bowl and press together to make one cohesive mass.
• Refrigerate streusel until ready to use.
• Combine apples, sugar, cinnamon, and nutmeg (if using) in an 8×8 baking dish. In a small bowl, make a cornstarch slurry by whisking 1 tbsp water with the cornstarch until cornstarch is dissolved. Add cornstarch slurry to apple mixture, and toss until combined. Remove streusel topping from refrigerator. Break up the large mass of streusel topping into pebble sized pieces and spread streusel topping over fruit.
• Bake crisp on middle rack in oven for 15 minutes. If streusel topping is getting too dark, loosely cover the crisp with foil for the duration of the cook time (you want the foil to be loose rather than tight so the streusel topping remains crunchy). Reduce oven temperature to 350 degrees and bake until the streusel topping is brown and fruit is tender, about 25-35 minutes more. 
• Serve apple crisp warm or at room temperature.