Apple-Rhubarb Crumble

This crumble is a perfect spring dessert.  We're still getting apples in our CSA box, but rhubarb has recently started turning up as well!  The two combine really well as the base for a crumble - the apples hold their shape and add sweetness, while the rhubarb melts down into a perfect sweet-tart mush.  I really like the simple topping here - it's full of oats and nuts for crunch, but it still forms together into nice clumps of tender pastry.  With a little lightly sweetened whipped cream on top, this crumble is heavenly!

Apple-Rhubarb Crumble (adapted from The Kitchn, original recipe here)

For the filling:
2 cups diced rhubarb (about 3-4 stalks)
4 cups peeled and diced apple (about 4 apples)
3/4 cup sugar
2 T lemon juice
3 T cornstarch
1 tsp ground vanilla beans (or substitute vanilla extract)

For the topping:
1 cup flour
1/2 cup rolled oats
1/2 cup chopped pecans
1/2 cup brown sugar
1 tsp baking powder
1/4 tsp salt
1 stick butter, softened

1. Preheat the oven to 375 degrees and lightly grease a 1-1/2 quart baking dish.
2. Toss together the fruit, sugar, lemon juice, cornstarch, and vanilla.  Scrape into the baking dish.
3. In a separate bowl, stir together the flour, oats, pecans, brown sugar, baking powder, and salt until well combined.  Cut the butter into several pieces and add to the flour mixture.  Work in with your fingers, a fork, or a pastry cutter until large crumbs form.  Sprinkle evenly over the fruit.
4. Bake the crumble for 25-30 minutes, until the filling is bubbly and the toppings is lightly browned.  Let cool about 15 minutes before serving.