Fill a deep pot with 1 inch of peanut oil and heat over medium heat to 350°F. Combine the cake flour, carbonated water, rice vinegar, and fish sauce in a small bowl. Mix until it just comes together, it should be runny and ribbony when it pours from the spoon.

Once the oil has heated up, take a spoonful of the batter and stream it into the hot oil until the pot is filled with little bits, but do not overcrowd. Cook in the oil until it turns a light golden brown. Remove the pieces with a fine mesh strainer and transfer to a plate with a paper towel. Repeat with the remaining batter.

Combine all of the ingredients for the sauce until smooth. Place in an airtight container and put in the refrigerator until you need it.

Combine the flour, salt, baking powder, and sugar in a large bowl. Whisk in the dashi stock until smooth. Cover and let rest at room temperature for one hour.

Add the egg and mix until it just comes together. Mix in the scallions, kizami beni shoga, and tenkasu.

Add the cabbage and fold in until well combined.

Heat a griddle over medium heat. Once heated, coat the pan with nonstick spray. Scoop a portion of the batter and shape into a 6-inch wide disc. Top with four pieces of pork belly.

Cover the pan and cook for four minutes, or until the bottom is browned. Using two spatulas, carefully but quickly flip the entire pancake over so the pork belly is on the bottom. If any pieces spread out of the disc, push it back into the disc.

Cover the pan again and cook for five minutes, or until the pork belly is cooked. Flip one more time, brush on the mustard okonomiyaki sauce, and cook for another two minutes, to crisp up the bottom a bit more. Transfer to a plate and top with additional mustard okonomiyaki sauce, japanese mayo, and aonori. Repeat with the remaining batter. This should make about three to four.