Preheat oven to 350°F. Line a 9x5-inch loaf pan with parchment and brush with 1 tbsp melted butter. Mash the bananas until mostly smooth.
In a medium bowl, whisk the flour, baking soda, and salt. In a large bowl, with hand mixer or stand mixer, beat the remaining butter, sugar, and egg until smooth. Beat in the milk and vanilla. Stir in the bananas.
Fold the flour mixture into the wet mixture, then gently fold in the berries. Transfer batter to lined pan. Bake 50 min., until toothpick inserted into center comes out clean. Cool 10 min. before removing from pan using parchment.
For even more texture and flavor, fold in ½ cup chopped pecans.