This Rhubarb Apple & Rum Crumble is a delightful dessert that combines the tartness of rhubarb with the sweetness of apples. The addition of rum adds a warm and rich flavor to the crumble. The crumble topping is buttery and crunchy, making it the perfect contrast to the soft fruit filling. Serve this crumble warm with a scoop of vanilla ice cream for a comforting and indulgent treat.