In a large bowl combine the melted butter, sugar, eggs, vanilla extract, and ¼ cup (2oz) of the cookie butter. Whisk until fully combined, make sure the creamy, thick cookie butter is fully combined.
Add flour, salt, baking soda, and baking powder then mix until just combined. Do not over-mix the dry ingredients, I use a spatula to gently fold the batter.
Pour half of the batter into the prepared loaf pan then spoon half of the remaining cookie butter on top of the batter and use a knife to swirl it. Top with remaining batter and repeat swirling of remaining cookie butter.