Prepare the Okonomi Sauce: In a small saucepan, combine 4 tbsp (60ml) ketchup, 2 tbsp (30ml) Worcestershire sauce, 1 tbsp (15ml) soy sauce, and 1 tbsp (15g) sugar. Heat over medium-low heat, stirring constantly, until the sugar dissolves and the sauce slightly thickens, about 3-5 minutes. Remove from heat and let cool. This makes more than needed for two servings.

Make the Okonomiyaki Batter: In a medium bowl, whisk together the all-purpose flour (120g / 1 cup), dashi powder (1 tsp / 5g), baking powder (1/2 tsp / 2g), and salt (1/4 tsp / 1.5g). Ensure there are no lumps.

Add the wet ingredients to the dry ingredients. Crack in the eggs (2 large) and pour in the water or dashi stock (150ml / 2/3 cup). Whisk until just combined to form a smooth, relatively thick batter. Do not overmix.

Prepare the Cabbage and Green Onions: Finely shred the green cabbage (300g / 3 cups). Thinly slice the green onions (2 stalks), separating the white and green parts if desired for different textures. Set aside.

Combine Batter and Fillings: Add the shredded cabbage and sliced green onions to the bowl with the batter. Gently fold them in using a spatula until evenly distributed. The mixture will be very thick and chunky.

Cook the Pork Belly (if using): Heat 1 tbsp (15ml) of vegetable oil in a large non-stick skillet or griddle over medium heat. Add the thinly sliced pork belly or bacon (100g / 3.5 oz) and cook until golden brown and slightly crispy, about 4-6 minutes per side. Remove the pork from the skillet and set aside on a paper towel-lined plate, leaving the rendered fat in the skillet.

Cook the First Okonomiyaki: Pour the remaining 1 tbsp (15ml) of vegetable oil into the skillet with the rendered pork fat (or add more oil if needed) and heat over medium heat. Spoon half of the Okonomiyaki batter mixture into the hot skillet, forming a round pancake about 15-20cm (6-8 inches) in diameter and 2-2.5cm (3/4 - 1 inch) thick. Gently spread it out if necessary.

Arrange Pork and Cook Underside: Lay half of the cooked pork belly slices (or raw bacon slices if you prefer them to cook with the pancake) evenly over the top of the uncooked batter. Cover the skillet with a lid or foil and cook for 5-7 minutes, or until the bottom is golden brown and firm. Carefully check the underside with a spatula to ensure it's not burning.

Flip the Okonomiyaki: This is the trickiest part! Slide a wide spatula underneath the pancake. With a swift, confident motion, flip the okonomiyaki over. If it breaks, don't worry, just gently press the pieces back together.

Cook the Second Side: Cook the flipped okonomiyaki for another 5-7 minutes, or until golden brown and cooked through. Press down gently with the spatula to ensure even cooking. The center should feel firm and spring back slightly when touched.

Repeat for Second Okonomiyaki: Slide the cooked okonomiyaki onto a serving plate. Add a little more oil to the skillet if needed, and repeat steps 7-10 to cook the second okonomiyaki with the remaining batter and pork.

Garnish and Serve: Drizzle generously with Okonomi sauce and Japanese mayonnaise in a zig-zag pattern over the top of each okonomiyaki. Sprinkle with bonito flakes (if using) and aonori (if using). Serve immediately while hot.