After just a few minutes with chef Nobu and his partner, Yuko, I felt like I was in a live taping of “I Love Lucy.” Yuko is highly animated, forceful, funny and charming. Her husband, Nobu, is a thoughtful introvert—the Ricky Ricardo to Yoku’s Lucy. All in all, it’s a match made in heaven.

And so is their restaurant, Kermis, which epitomizes what is so special about the Tokyo dining scene: Restaurants tend to be small with a bare minimum of build-out investment so a young couple might get into the business for short money. This gives Tokyo nightlife a terrific advantage over New York or San Francisco, where the startup costs are near prohibitive. With low overhead, Nobu and Yuko can go on vacation, take a long weekend, and spend more time cooking than worrying about making ends meet.

One of the two dishes that Nobu taught me was his version of chan chan yaki, a simple Hokkaido-­style dish of skinless salmon with vegetables (cabbage, oyster and enoki mushrooms, scallions and red pepper), dressed with a salty-sweet miso-­based sauce and finished with butter. (There’s a lot of butter in Hokkaido-style cooking.)

The salmon mixture is wrapped in foil as if it were parchment paper, then baked. Originally, the dish was cooked on a griddle—the name chan chan is onomatopoeic, echoing the clack of spatulas on hot metal—but sautéed, stir-fried and, like ours, steam-roasted variations abound.

During my 10 days in Japan, I became interested in mirin, which is used as frequently as soy sauce and sake. Real mirin, known as hon mirin, is made by fermenting glutinous rice with koji (a mold that grows on rice) and shochu (a type of distilled alcohol). Hon mirin has an alcohol content of roughly 15 percent and the flavor is complex. Aji mirin, on the other hand, represents a cheaper, more industrial production method. It is flavored with additives such as sugar, corn syrup and salt. Here in the USA, many supermarket mirins are aji mirins. These list glucose, water and alcohol as the first three ingredients in what can only be called a bad sign. A good-quality hon mirin, by comparison, has an ingredient list that reads: organic rice, organic rice wine and organic koji. No glucose!

This contrast led us to a full-blown blind tasting, which included a few substitutes that might be better than supermarket mirin in a pinch. The winner was a traditional hon mirin (Yoneda). The aji mirin did okay when buried in a stew, but performed poorly in simpler dishes. No surprises so far. Some sweetened rice wines performed well, but a combination of maple syrup and sake (a notion suggested to us in Japan) was our favorite substitute. Seasoned mirins were often found to be too salty—less of a problem in complex dishes than in simple dressings. Sweet Reisling, Sauvignon Blanc and fortified wines like sherry performed badly, as did sweeteners such as honey and agave. The worst substitute was simple syrup, which proved on par with a poor-quality aji mirin.

Back at Kermis, the foil packet came out of the 350°F oven after 20 minutes. The foil was opened and Nobu added a pat of butter to melt into the sauce of miso, sake, mirin, shoyu and brown sugar. Much like in French cuisine, but with more subtlety, this dish showcases the power of a good sauce. Various combinations of soy, mirin, sake, miso and sugar transform the simplest ingredients into something more complex and more interesting. The main ingredients are supported by the sauce, not cloaked by it, which is a culinary lesson worth taking to heart.

Christopher Kimball

Christopher Kimball is founder of Milk Street, which produces Milk Street Magazine, Milk Street Television on PBS, and the weekly public radio show Milk Street Radio. He founded Cook’s Magazine in 1980 and was host and executive producer of America’s Test Kitchen until 2016. Kimball is the author of several books, including "The Yellow Farmhouse" and "Fannie’s Last Supper."