Cover crumble with the mixed berries. Sprinkle remaining crumble over the berries. Place in the preheated oven and bake until the fruit is bubbly and the top is golden brown; about 30-40 mins.
Sprinkle with cake mix and almonds. Cut butter into very thin slices; arrange over top, spacing evenly. Bake until golden brown and fruit is bubbly, 35-40 minutes. Serve warm.