1) Preheat the oven to 350°F. Lightly grease a 9" round or 8" square pan.
2) To prepare the blueberries: Place the berries in a microwave-safe bowl, and heat them for 4 to 5 minutes, until they're thawed and beginning to warm. Do this if you're using fresh berries, as well; it helps get their juices going.
3) Combine the berries with the remaining filling ingredients, and spoon the mixture into the prepared pan.
4) Place the pan in the oven, and bake the blueberries for 30 minutes, until they start to bubble. While they're baking, prepare the topping.
5) To prepare the topping: Whisk together the dry ingredients. Add the melted butter and flavors, mixing until coarse crumbs form.
6) Remove the berries from the oven, and spread the topping on tops. Bake for an additional 45 minutes, until the berries are bubbling and the topping is beginning to brown. Some of the topping will have been engulfed by blueberry juice, leaving your crisp with a somewhat mottled top; this is perfectly fine.
7) Remove the crisp from the oven, and allow it to cool completely before serving. If you serve the crisp right away, it'll be very liquid; letting it to set up allows the berries to reabsorb some of their juices.
8) Serve the crisp plain, or à la mode. Heat it briefly (about 30 seconds) in the microwave, if desired, to provide a nice warm bed for the ice cream!
Yield: 8 to 10 servings.