01 - Preheat oven to 350°F. Lightly grease a 2-quart baking dish with butter or nonstick spray.
02 - In a large bowl, gently toss the mixed berries with granulated sugar, cornstarch, lemon juice, and 1 teaspoon vanilla extract until evenly coated. Spread the berry mixture in an even layer across the bottom of the prepared baking dish.
03 - In a separate bowl, combine the rolled oats, all-purpose flour, sliced almonds, packed brown sugar, and salt. Stir until evenly mixed.
04 - Add the cold cubed butter and remaining 1/2 teaspoon vanilla extract to the dry mixture. Using your fingers or a pastry cutter, work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized butter pieces remaining.
05 - Evenly sprinkle the almond-oat topping over the berry filling, covering the surface completely.
06 - Bake for 35 to 40 minutes, until the topping is deep golden brown and the berry juices are bubbling around the edges.
07 - Allow the crisp to rest for 10 to 15 minutes before serving. Serve warm, optionally topped with vanilla ice cream or freshly whipped cream.