Make the Dough: Add the flour, sugar and salt to a mixing bowl then combine them together. Add the cold cubed butter and chopped shortening. Using your fingers, coat the butter and shortening in the flour then press the pieces of fat into flat disc shapes. Once the pieces of fat are flat, slightly break them up further until you have small peas size pieces of fat throughout the mixture. It is ok to have some larger pieces.
To a jug, add the cold water, ice cubes and lemon juice. Make a well in the centre of the mixture then pour around half of the water into the centre. Using both hands, begin to toss the flour and water to help the pastry come together. Continue to add more water in teaspoon increments while still bringing the dough together to form a ball. If bits of dough are falling off. Dip your fingers into the water and slightly wet the area you want to attach it to rather than pouring more water in. At this point the dough should not be sticky but not dry either.
Once you form a dough, flour a clean surface and tip the dough onto the surface. Gently knead the dough but don’t overdo the kneading and just knead enough to keep the dough together. Flatten the dough and form into a disk shape then wrap in cling film and refrigerate for 1 hour.
Make the Pie Filling: While the dough is in the fridge, you can make the pie filling. Wash the cherries and blueberries then remove the pits from the cherries. You can do this by hand but its quicker to use a cherry pitter. Add the fruit to a small saucepan then add the lemon juice, sugar, vanilla extract and cornflour. Mix all the ingredients together until the cornflour dissolves.
Place the saucepan on a low heat to cook the fruit. As the blueberries and cherry’s start to release their juices, begin to stir the fruit occasionally to prevent it from burning. Once the fruit is soft and the juice has thickened, remove from the heat and allow to completely cool. This process should take around 12 minutes.
Assemble the Pies: Preheat the oven to gas mark 4/350oF/180oC/160oC fan and grease a 6-count muffin tin. Lightly flour a surface and begin to roll out the dough. When it reaches around ½ cm thick, cut 6 circles using a cookie cutter. Carefully place each circle into the cups of the muffin tin. Now re-roll the dough if necessary and cut strips to make the lattice pie tops.
Make a egg wash by whisking together the egg and milk. Add the pie filling to the cupped pastry. Brush the rim of each pie with the egg wash then arrange the pastry strips to form lattice shapes on top of the pies. Trim of any overhang then brush the top of the pies with the egg wash, sprinkle on some granulated sugar and then bake the pies for 30 minutes. Allow the pies to cool in the tins for 10 - 15 minutes then carefully remove from the tins and allow to completely cool on a cooling rack.