For the pastry, in the bowl of your mixer fitted with the paddle attachment, mix the flour, sugar, butter and salt until a breadcrumb consistency is reached.
To this add the yolk and water and mix until a dough is reached.
Turn this onto a floured table and gently work, wrap in clingfilm and chill for 30 minutes.
For the filling, in a pot gently cook the chopped rhubarb with the sugar and water until the rhubarb begins to soften, take off the heat.
Once the pastry is rested, knead on a floured surface until smooth. Roll into a circle and using the rolling pin, transfer this onto a lined baking tray.
Spoon the rhubarb into the centre and top with the strawberries, leaving a 2 inch rim around the edge.
Carefully fold the edges inward on top of the fruit leaving some of the centre fruit exposed.
Egg wash the pastry and place in a preheated oven at 180C/160C fan and bake for 35-40 minutes or until golden brown.