Rinse the anchovies, remove the heads, and clean out the innards and spine with your fingers. The fish should open neatly and feel clean inside, with the tail still attached if you want the classic butterflied shape.

Mix the flour, salt, and black pepper on a large plate or in a wide bowl until the seasoning is evenly distributed. An even dredge means the fish fry up crisp and properly seasoned instead of patchy or bland.

Toss the cleaned anchovies in the seasoned flour until they are fully coated, then shake off any excess. The surface should look dry and dusty rather than wet or pasty.

Pour the vegetable oil into a small saucepan so it is a few inches deep, then heat it and test with the tip of a toothpick. If small bubbles form almost at once, the oil is hot enough to fry.

Lower a few floured anchovies into the hot oil with a slotted metal spoon or metal spatula, leaving space around each one. The bubbling will start fast and loud, which is a good sign that moisture is escaping and the crust is setting.

Fry the anchovies for about 1 minute until golden brown. As they finish, the bubbling calms down and the fish look crisp rather than pale.

Lift the anchovies out with metal tongs or a metal slotted spoon and transfer them to a paper towel-lined plate. The crust should feel light and crisp right away, not heavy or oily.

Add enough oil to a pan to reach about 1/2-inch deep, then heat it and check it with the toothpick test. The oil is ready when it reacts quickly with tiny bubbles instead of sitting still.

Lay in the floured anchovies without crowding the pan and cook for about 30 seconds to 1 minute per side. Turn them when the first side looks golden and releases easily from the pan.

Move the cooked anchovies to a clean paper towel-lined plate. They should be crisp outside and still delicate inside, not dark or dried out.

Serve the fried anchovies warm with fresh lemon juice squeezed over the top and tartar sauce on the side. The lemon wakes up the flavor immediately and balances the fried coating.

Stir together the mayonnaise, sweet pickle relish, lemon juice, and any optional seasonings for the tartar sauce, then taste and adjust. The finished sauce should taste creamy, tangy, and bright enough to cut the richness of the fish.