Place the ready-rolled shortcrust pastry into a round 9-inch tart tin, and seal in the sides gently by pressing the pastry to the edges of the dish with your fingers. Use a knife to cut off the excess pastry.
In a bowl, combine together the strawberries, rhubarb, sugar, flour, nutmeg, and cinnamon.
In a separate bowl, whisk together the milk and the eggs.
Pour the egg mixture into the strawberry and rhubarb mixture and combine. Then pour the mixture into the prepared pastry base.
Dot the top of the tart with cubes of butter
Bake for 1 hour until set.
Allow the tart to cool completely before serving. Sprinkle with pistachios if desired.