Preheat the oven to 350F and line a standard muffin tin with 12 baking cups. (I use these reusable silicone cups.) In a large mixing bowl use a fork to mash the ripe bananas until they have a puree-like consistency-- it's okay if there are a few lumps. Add in the peanut butter, buckwheat flour, maple syrup, salt, and baking soda and mix well until a sticky batter is created, then stir in the vinegar last. Fold in the fresh raspberries and divide the batter between the 12 muffin cups.
Bake until the centers are firm and the tops begin to crack, about 20 minutes. Cool completely in the pan before serving, and store the muffins in a sealed container in the fridge for up to a week.