Preheat your oven to 350ºF and prepare a muffin tin with 12 muffin liners.
In a medium bowl, combine the peanut butter, mashed banana, baking soda, vanilla, eggs, salt, honey, and cinnamon, if using, and mix until smooth. I like to use a whisk to make sure the ingredients are evenly incorporated. Fold in one of the optional add-ins, if desired.
Divide the batter among the 12 muffin cups. Using a 1/4 cup measure should distribute the batter pretty evenly.
Bake at 350ºF until the muffins have risen, and feel firm to a light touch in the center of the muffin, about 20 to 25 minutes.
Allow to cool for at least 30 minutes before removing from the pan.
These muffins can be served at room temperature once they have cooled, but I recommend storing them in the fridge for the best shelf life. They should last for up to a week in the fridge when stored in an airtight container. You can freeze them for up to 3 months in an airtight container, too.
Almond butter can easily be substituted for the peanut butter in this recipe, if you prefer. You could also try sunflower butter as a nut-free option!
I don't recommend substituting the eggs in this recipe. For an egg-free option, be sure to read the suggestions below this recipe.