Place everything in a bowl and use your fingers to pinch the ingredients together. You can also do this in a food processor.
Stop when there are no lumps of butter and the mix looks like wet sand.
Sprinkle the crumble over the tart.
Bake the tart in a preheated oven at 180°C / 350°F for 15-20 minutes or until the crumble is golden.
Remove it from the oven and wait for it to cool down before cutting.