Look beyond the excellent, bargain-priced yellowtail and white tuna on the menu at Kotobuki, a cozy sushi spot in DC's Palisades, and your eye might fall on a type of sushi that's far less common in the States. Oshizushi--sushi in the Osaka style--is marinated fish pressed into a bed of vinegared rice. It's a method of sushi-making that dates back hundreds of years, long before refrigeration.

In Japan, oshizushi might be made with mackerel, eel, or sardine. Chef Hisaoka Abe likes Atlantic mackerel, a fish that's fattiest and most flavorful in the winter. Using a long knife, Abe slices the head and tail from the silver mackerel, then slides the knife along its skeleton, producing two filets in less than a minute. He lays the fish in salt for 20 minutes to remove some of its moisture, then in rice vinegar for another 20, and peels off its tough skin. At a sushi bar, only one ingredient is as important as the fish: the rice. And every sushi chef has his own way of making it. At Kotobuki, Abe flavors his steaming tubs of Tamaki Gold, a California short-grain rice, with bonito, sugar, salt, sake, and rice vinegar.

When an order comes in for oshizushi, Abe reaches for a cedar box. He tamps a thick layer of rice into the bottom, then lays a mackerel filet on top. Standing on his toes, with the heels of his hands he presses the box's lid down on the fish, then lifts out a beautifully clean rectangle. He slips an amber sheet of marinated seaweed on top and slices it.

Mackerel, it can be argued, is an acquired taste--oilier and more potent than most fish. But at Kotobuki its butteriness is focused, and its fishiness is tamed by the sweet seaweed and sharply vinegared rice. Like the restaurant itself, it's an unexpected gem.