Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a large bowl, whisk melted butter, brown sugar, eggs, and vanilla extract together until smooth. Add in the flour, salt, and baking powder until smooth.
Fold in the fruity pebbles cereal. Evenly divide the batter between the prepared muffin pan. Bake for 15-20 minutes.