01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease each cup.
02 - In a large skillet over medium heat, melt 1 tablespoon of the butter. Add mushrooms and onion; cook until vegetables are soft and most liquid has evaporated, about 6 to 8 minutes. Stir in soy sauce and cook for 1 minute longer. Remove from heat; allow mixture to cool.
03 - In a large bowl, whisk together all-purpose flour, baking powder, baking soda, salt, and black pepper until well combined.
04 - In a separate bowl, whisk together whole milk, eggs, Greek yogurt, and remaining melted butter until smooth.
05 - Fold wet ingredients into dry ingredients just until combined. Gently mix in cooled mushroom mixture, grated cheese, sliced spring onions, and 2 tablespoons furikake seasoning. Do not overmix.
06 - Spoon batter evenly into prepared muffin cups. Sprinkle each muffin with extra furikake and toasted sesame seeds.
07 - Bake muffins for 22 to 25 minutes, or until tops are golden brown and a toothpick inserted in the center comes out clean.
08 - Leave muffins in tin for 5 minutes, then transfer to wire rack to cool completely. Serve warm or at room temperature.