5 sticks rhubarb, cut into 3cm pieces
1 tsp cinnamon
3 tbsp plain flour, plus extra for dusting
5 tbsp soft brown sugar
½ a 500g block puff pastry
3 tbsp unsalted butter
50g rolled oats
Heat oven to 200C/fan 180C/gas 6. In a bowl, toss the rhubarb with cinnamon, 1 tbsp flour and 2 tbsp sugar. Line a baking sheet with a piece of baking parchment.
If using apples and blackberries, thinly slice the apples and wash the blackberries.
Roll out the pastry on a floured surface to approx 20 x 30cm, then cut into quarters and place on the sheet.
Rub together the remaining flour, sugar, butter and oats to make a rough crumble mixture.
Divide the rhubarb between the pastry quarters, or space out the apple slices and blackberries, leaving a 1cm rim.
Sprinkle the oat mixture over, then fold and pinch each corner to keep the filling in. Bake for 20-25 mins, then serve warm.
If cooking on the clay oven, wait for the temperature to drop slightly before cooking.