Preheat the oven to 165˚C.
In a sauté pan, over medium heat, melt the brown sugar with 50g butter and add the rhubarb, and apple and lemon juice. Simmer for 5 minutes until the apple are cooked through and the rhubarb has started to breakdown.
In the meantime, line a tart tin with the sweet pastry. Keep refrigerated until needed.
Next, in a bowl, Sift the flour with the caster sugar, 50g of butter, porridge and baking powder. Combine together until the mixture resembles crumbles.
Add the apple and rhubarb mixture in the cooled pastry base and brush the edges with egg wash. Sprinkle the crumble over to cover the tart.
Carefully place in the oven and cook for 40-45 minutes until the pastry is cooked through.
Remove from oven and leave aside for 10-15 minutes for the tart to settle.
serve warm or at room temperature with some extra whipped cream.
Apple and Rhubarb crumble Tart