Preheat the oven to 180°c / 160°c fan. Place the cut rhubarb on a baking tray, sprinkle with water and 2 tbsp caster sugar, then place the tray in the oven and roast for 10 minutes. Remove from the oven and allow to cool. Whilst the rhubarb is roasting, rub together the flour, butter, and demerara sugar in a large bowl to create the crumble topping then
set aside. In a large, oven-proof dish, add the sliced apples, sprinkle over 4 tbsp caster sugar and then add several dollops of Mrs Bridges Rhubarb & Ginger Preserve. Next, add the roasted rhubarb, a few more spoonfuls of the preserve, and the remaining caster sugar before sprinkling the ground ginger over the top. Evenly cover with the crumble topping and place in the oven to bake for 35 - 45 minutes, or until the crumble topping is golden brown and you can see the fruit bubbling.