Preheat oven to 350°F and line the muffin pan with tulip baking liners
Combine dry ingredients and mix together: flour, granulated sugar, brown sugar, salt, cinnamon, nutmeg, baking powder, baking soda
Combine wet ingredients and mix together: bananas, eggs, vanilla extract, and butter
Add wet ingredients to the dry mixture and whisk until there are no lumps. Don't over mix
Chop walnuts (or preferred nuts) and fold into batter
Fill baking liners with batter until they are full. Tip: the batter should fill the entire muffin pan, leaving about an inch of the liners exposed
(Optional) In a small pan over medium heat, add your butter, chopped walnuts and a dash of cinnamon. Toast for about 2-3 minutes, then top the muffins and sprinkle with flakey sea salt
Bake for 20-25 minutes or until center is set. To test doneness, insert a toothpick or butter knife and make sure it's either dry or crumbly. If it's still wet, pop them back in until done
Let cool for 5-10 minutes, top with some butter spread, and enjoy!