Sift the ＊ ingredients, then stir in the whole wheat flour. Bring the butter to room temperature to soften. Also bring the milk to room temperature.
Mash the bananas with a fork, then add the vinegar (to prevent discoloring).
Chop the walnuts and roast in the oven for about 10 minutes at 140℃. (No need to preheat the oven.)
Heat the egg to body temperature in a hot water bath. This will prevent separation. Preheat the oven to 180℃.
Use a whisk to cream the butter in a large bowl. If it's too hard, soften in a hot water bath for 1 to 2 seconds at a time.
When the butter is completely smooth, add brown sugar (or light brown sugar), and mix. Use a whisk to whip until fluffy.
Add the egg in 5 to 6 batches, mixing thoroughly after each addition. It will separate if mixed too quickly, so mix slowly.
Add 1/3 the sifted ＊ ingredients, then briskly stir by scooping the batter from the bottom in a cutting motion.
Add 1/2 of the milk, and briskly stir it in. Alternate mixing in 1/3 of the dry ingredients, the rest of the milk, finishing with 1/3 of the dry ingredients.
While the flouriness of the flour remains, add the mashed bananas from Step 2, and lightly fold in.
Add the walnuts from Step 3, and lightly fold in.
Fill the muffin tray with paper cups, then bake for 20 to 25 minutes at 180℃. If it looks like the muffin tops might burn, cover with aluminum foil.
Since they are filled with bananas, they're fragrant. The walnuts are also crunchy and give a nice aroma. I recommend using ripe bananas.
Story Behind this Recipe
I love the combination of bananas and walnuts. By adding whole wheat flour, I created a rustic tasting muffin.
-Do not sift the whole wheat flour. -Chop the walnuts however you like. I chop them into slightly large pieces. -To prevent the bananas from discoloring, vinegar is better than lemon juice, since it doesn't leave a smell after baking. -You can also bake these in other molds or aluminum muffin cups.