Step 1

Combine cabbage, scallion whites and half of greens, half of beni-shoga, 3/4 of katsuobushi, yamaimo, eggs, and water (or dashi) in a large bowl. Sprinkle with flour. Stir with a fork and beat heavily until a thick batter with plenty of bubbles forms. Set aside.

Step 2

If using pork belly, cover the bottom of a 10-inch nonstick skillet with pork belly and set over medium heat. Add okonomiyaki mixture and spread into an even layer with a fork. If not using pork belly, heat vegetable oil in skillet over medium heat until shimmering. Add okonomiyaki mixture and spread into an even layer with a fork.

Step 3

Cover and cook, shaking pan occasionally, until bottom layer is crisp and well browned, about 10 minutes, lowering heat as necessary if cabbage threatens to burn.

Step 4

To flip, drain off any excess fat, then, working over a sink and holding the lid tightly against pan with a pot holder, flip entire pan and lid over so that okonomiyaki transfers to pan lid. Remove pan, then carefully slide okonomiyaki off lid and back into pan, browned side up.

Step 5

Return to heat, cover, and continue to cook, shaking gently, until both sides are browned and okonomiyaki is not runny but still custardy and tender in the center, about 8 minutes longer. Transfer to a serving platter, pork side up.

Step 6

Drizzle with okonomiyaki sauce and mayonnaise; sprinkle with ao-nori, remaining beni-shoga, remaining katsuobushi, and remaining scallion greens; and serve immediately off of a communal plate.