In a large bowl, combine 2 cups all-purpose flour, 1 1/2 teaspoons baking soda, and 1/2 teaspoon salt; set aside. In a small bowl, mash 2 overripe bananas with a fork so they have a bit of texture; set aside.
With an electric mixer, whip together 2 more overripe bananas and 1 cup brown sugar for 3 minutes. Add 3/4 cup unsalted butter (melted and cooled), 2 eggs, and 1 teaspoon vanilla and beat well, scraping down the sides of the bowl once or twice. Mix in thedry ingredients until just incorporated. Fold in 1/2 cup chopped pecans and the mashed bananas with a rubber spatula.
Spoon the batter into prepared muffin tins, filling them about halfway. Rap tins on the counter to get any air bubbles out. Bake until a toothpick inserted in the muffins comes out clean, around 18 to 20 minutes. Let cool for a few minutes before turning the muffins out. Enjoy warm or at room temperature.