I keep my pantry stocked with an obscene number of sardine tins. While other people sate an urgent hunger with nuts or toast or an energy bar, I peel back a rectangular can's lid, trying not to slosh fishy oil onto my counter, then stand over the sink and slide each sardine whole into my mouth—like a seal at the circus, a new fish is on its way in before I've managed to swallow the one before.
But canned sardines, as much as I love them, are a poor substitute in dishes that call for fresh ones. Thanks to the canning process, they're too well done and dry to handle the additional cooking that a recipe intended for fresh sardines requires. Many years ago, this was rarely of any consequence; good luck finding fresh sardines anyway. But times change and now whole fresh sardines are commonly laid out on the fishmonger's display (at least, this is true where I live in New York City).
To buy fresh whole sardines, though, you need the confidence and know-how to clean and prep them, a task I'd imagine scares away a lot of potential customers. You could ask the fishmonger to do it for you. But more so than most fish, sardines have delicate flesh that can quickly become smashed and smushed, especially once it's off the bone and wrapped in paper to take home. That means you really are better off doing it yourself.
There are several ways to clean and fillet a sardine, some of which require the knife skills of a sushi chef (not to mention a knife as sharp as the ones those chefs keep—good luck filleting a sardine with an even slightly dull blade). Fortunately, there's also a way that requires no knife at all, just a pair of scissors and your hands. It's a technique I learned from the chef Seamus Mullen several years ago, and while the results aren't quite as pristine as you'd want if you were serving the fish raw on rice, they're more than adequate for most cooked applications.
Start With Good Fish
Before you buy and clean your sardines, you want to make sure they're in good condition. That means bright, silvery skin and flesh that's still firm without any signs of mushiness—telltale indicators include bruised and smashed spots on the skin, and a belly that's starting to come undone all on its own.
Sardines are an oily fish, so to some degree they're going to smell fishy no matter what, but it should be the best possible version of that fishy smell, not unpleasant or stinky.
Finally, as with most fish, the eyes are a good indicator of freshness: clear, plump eyes (not cloudy and sunken) are best.
Step 1: Rinse off Scales
Under gently running cold water, rinse the sardines. Using the cutting edge on an open pair of kitchen scissors, gently clean away the scales, scraping from the tail up towards the head. Take care here, because too much pressure can tear the skin. Sardine scales are tiny and not too hard, so it's better to leave a few behind than to gouge the skin and flesh with overzealous scaling.
Step 2: Cut Off the Head
Using the same pair of scissors, snip off the head behind the gills. Do this at a slight angle so that you also snip off the small pectoral fins on each side.
Step 3: Cut Open the Belly
Now take the scissors and snip the belly open, starting at the opening where the head used to be.
Step 4: Remove the Dorsal Fin
Using your fingers, pinch the dorsal fin and pull it free from the fish. This fin has bones that are usually a little too big to eat, so you want them out.
Step 5: Clean Out the Belly
Using your fingers, scrape out the contents of the belly. Rinse the cleaned cavity under gently running cold water, scraping out any blood, membranes, or viscera clinging to the inside.
Step 6: Pull Out the Backbone
Spread the belly cavity open and find the spine: It runs right along the top side of the belly from the neck, then continues all the way down to the tail. Using your fingers, carefully pinch the spine, pulling it free of the surrounding flesh. It should pull free fairly easily, but take care not to gouge the flesh as you go; this is relatively easy to do, but if you're in too much of a rush or aren't paying attention you can tear up the fillets.
Work the spine clear of the flesh all the way down to the tail, then snap it free.
You now have a butterflied sardine, free of the spine and any larger rib bones (most sardine bones are too small to matter, so don't worry about getting them out). You can stop here depending on your preference or the recipe: At this stage the sardines can be stuffed, rolled, or skewered for cooking.
Or, you can continue to clean them further.
Step 7: If Desired, Trim the Butterflied Sardine
If you want to clean the sardine more, you can use your scissors to trim the belly flaps and neck end for a nicer presentation. You can also snip off the tail, if desired.
Step 8: Divide the Fillets
For individual fillets, simply take you scissors and snip the two fillets apart right along the seam that joins them.
That's it. At this point, you can leave the fillets whole or cut them up into smaller pieces, depending on your recipe.