Preheat the oven to 350°F and line a muffin tin with liners
In a large mixing bowl, mix together mashed bananas, melted coconut oil, granulated sugar, vanilla and egg until well combined and creamy.
In a separate bowl, whisk together the flour, baking soda, baking powder, salt and cinnamon
Slowly add the dry ingredients to your wet ingredients, alternating with milk. Mix until just combined, it is okay to have some lumps in your batter.
Put 1/2 cup cookie butter in the microwave for about 20 seconds to soften it. Then, gently add spoonfuls of cookie butter to your muffin batter, and use a knife to slowly swirl the cookie butter around.
Carefully spoon batter into lined muffin tin until cups are about 3/4 of the way full.
Optional cookie butter filling: Using the small end of a melon baller, place a dollop of cookie butter in the center of each muffin cup with batter.
Bake for 18-20 minutes, or until a toothpick inserted comes out cleanly.
