Pastry Dough:

• In a medium bowl, combine flour and salt. Grate cold butter into the flour bowl and mix together. Gradually add the ice cold water and vinegar mixture to the flour and butter mixture, stirring the dough around the bowl with a fork or your hands to bring the dough together. As soon as it is moist enough to gather the dough together, form the dough into 1 large disc and tightly wrap in plastic wrap and place in the refrigerate for minimum 30 minutes or overnight. Handle the dough as little as possible, as over mixing will cause the dough to become tough.
• While dough is chilling, prepare the filling and crumble mixture. In a large bowl, using a spatula, gently mix together diced rhubarb, sugar, flour and cinnamon.
• In a large bowl, mix together flour, oats, brown sugar, cinnamon and melted butter. Spread evenly over the rhubarb mixture.
• Pre-heat oven to 350°F.
• Take dough out of the refrigerator and roll it out to fit the 9 inch pie plate. Always measure by placing the pie plate over the rolled out dough. To consider the depth of the pie plate, measure 2-3 inch beyond the pie plate. Create a decorated pie by fluting the edges of the dough. Whisk the egg in a small bowl and brush the edges of the pie with a pastry brush.
• Add the rhubarb filling to the prepared pie plate and add the crumble evenly over the filling. Bake for 50 minutes. Allow to cool on a cooling rack.
• Enjoy! Serve warm with ice cream.