Banana-Nut Muffins
1 cup chopped pecans, divided, or as needed 1 tablespoon ground cinnamon 1 teaspoon pure vanilla extract 1 ½ sticks unsalted butter, melted and cooled 1 ½ teaspoons baking powder 2 cups all-purpose flour 2 cups brown sugar 2 eggs 4 overripe bananas, divided ¼ cup white sugar ½ teaspoon baking soda ½ teaspoon salt