01 - Preheat the oven to 350°F. Lightly grease an 8×8-inch baking dish with butter or nonstick spray.
02 - In a large bowl, toss the mixed berries with granulated sugar (or honey), lemon juice, vanilla extract, and cornstarch until evenly coated. Spread the mixture in an even layer across the bottom of the prepared baking dish.
03 - In a separate bowl, combine the rolled oats, almond flour, sliced almonds, brown sugar, cinnamon, and salt. Pour in the melted butter and vanilla extract, stirring until the mixture forms moist, crumbly clusters.
04 - Scatter the crumble topping evenly over the berry filling, ensuring full coverage across the surface.
05 - Bake for 35 minutes, or until the topping is deep golden brown and the berry juices are bubbling around the edges.
06 - Allow the bake to rest for 5 to 10 minutes before serving. Serve warm on its own or paired with a dollop of yogurt or vanilla ice cream.