Preheat oven to 350°F. Grease or line a loaf pan with parchment paper and set aside.
In a large bowl, mix together mashed bananas, maple syrup, almond butter, vinegar, milk, and almond extract.
In a separate bowl, whisk flour, baking soda, cinnamon, nutmeg, and salt.
Add flour mixture into the banana mixture, and use a rubber spatula to gently fold together. Mix until ingredients are almost incorporated (some dry flour pockets are OK at this point), add walnuts, and gently fold a couple more times to evenly distribute the walnuts. At this point no flour streaks should remain. Be sure to scrape down the sides and the bottom of the bowl for dry flour.
Pour batter into the prepared loaf pan. Bake for 60 minutes**, or until a toothpick inserted in the center of the loaf comes out clean. After 30 minutes, keep an eye on the bread to make sure it's not browning too quickly on top. If it looks like the top is starting to burn, tent with foil.
Let the bread cool for about 5 minutes in the pan, then transfer to a cooling rack. Cool completely before serving.
Notes
Baking Time: For a 9" loaf pan, it takes about 60 minutes in my oven. For an 8" loaf pan, it takes 75-90 minutes in my oven.