If you have the time, heat a non-stick frying pan over a high heat on the hob, then place the chorizo in the pan and sear until browned on both sides. If you’re in a hurry, just skip this step.
Reserving a few slices of chorizo for garnish, place all the ingredients in the slow cooker, stir and season to taste. Cook on high for 3 hours, then blitz the soup with a handheld blender until smooth. Garnish with the reserved chorizo and a sprinkle of chilli flakes.