Prepare the avocado just before you want to cook the cakes, as it discolours if it sits too long. Halve and stone the avocados and scoop out the flesh. Mash with all the other ingredients until smooth. Taste for seasoning (you may want to add a little more vinegar). Cover and set aside.

For the fritters, put the cornmeal, flour, half the sweetcorn, the eggs, milk, butter and baking powder in a food processor and, using the pulse button, blitz together. Season and stir in the rest of the corn, the chipotle paste, chilli, spring onions and the prawns by hand.

Heat some oil in a large frying pan and, once it is hot but not smoking, spoon dollops of the corn-cake batter into the pan. You are aiming to make cakes about 10cm in diameter. If you use a large pan, you should be able to cook four fritters at the same time. When each cake has set underneath and you can see bubbles on the surface, flip it over and cook until golden. Lift each cake out onto a double layer of kitchen paper. You can keep the cakes warm on a baking sheet (in a single layer) in a low oven while you cook the rest. Add more oil as you need it. Serve the cakes with the avocado purée, some soured cream and wedges of lime.