Add the chopped rhubarb, caster sugar and a pinch of salt to a large saucepan.
Place the saucepan over medium heat and cook the rhubarb for 5 to 7 minutes until soft. Just let the rhubarb and sugar sweat for a while and stir regularly. Keep an eye on it though to make sure that the melted sugar is not burning! In the end stir in the strawberry jam. You can also add a drop of red food coloring if you want.
Then take the rhubarb puree off the heat and place it aside until cooled down. In the meantime chop the pistachios roughly and add them together with the brown sugar, self-raising flour, a pinch of salt and the diced cold butter to a large mixing bowl. Rub these 5 ingredients together between your fingers until you get a crumbly and lumpy mixture.
Scoop the cooled rhubarb and strawberry mixture into small ramekins. Top them evenly with the pistachio crumble.
Bake the rhubarb crumbles in a preheated oven at 356°F (180°C) for 25 minutes or until the pistachio crumble on top looks golden. Put a piece of tinfoil on top if it browns too fast. Remove the rhubarb crumble from the hot oven and let them cool a little because the rhubarb underneath the crumble layer is blazing hot. Serve lukewarm.