Bring the butter, egg and milk to room temperature. Preheat the oven to 180℃. Break each square of chocolate into 4 pieces. Toast the walnuts in the oven while preheating and crush lightly after they've cooled slightly.
Put the A ingredients in a large bowl and mix well with a whisk.
Cream the butter in a separate bowl with a whisk, add the sugar and egg and blend well. Mix in the milk and vanilla essence.
Fold the ingredients from Step 3 into Step 2 with a spatula, mixing just until the flour is incorporated. (Do not over mix.) Lightly mix in the walnuts and broken chocolate.
Fill the muffin cups about 80% full. Smooth the tops and bake at 180℃ for 20~25 minutes. They're done when a bamboo skewer comes out clean. Cool on a rack.
Story Behind this Recipe
I often made muffins on the weekends. To tell the truth, I really wanted to make American-style muffins, so I modified recipes from "Allrecipes" and cookbooks, but they never turned out well. When I modified American recipes, they tasted Japanese. If you cut the amount of butter and sugar any more, they won't taste good, so this is the final version.
If you use 80 g cake flour＋20 g whole wheat flour, instead of 100 g cake flour, they are nice and crisp.