Melt the butter in a frying pan over a medium heat. Add the kippers and cook gently skin side down for 3 minutes, then flip and cook on the other side for 2 minutes.
Meanwhile, finely slice the fennel bulb.
Toast your sourdough - either in a toaster or under a grill - until just crisp.
Spread one tablespoon of crème fraiche on each slice of bread. Share the fennel evenly between the two slices, then top each one with a kipper. Enjoy!