Preheat oven to 375 °F. Line muffin tin with cupcake liners. Set aside.
In a large bowl, whisk together flour, sugar, salt, baking powder, and baking soda.
In another bowl, combine melted butter, whisked egg, and buttermilk. Add to dry mixture. Stir together using a sturdy spatula.
Add mashed bananas and stir until incorporated. Gently fold in raspberries.
Use an ice cream scooper to distribute batter among prepare muffin tin. Fill tins a little over ¾ full.
Bake for 18-22 minutes until muffins are golden brown and toothpick inserted in center of muffin comes out clean. Let cool in tin for 3-5 minutes. Unmold and allow to cool to room temperature on wire rack. Garnish with sifted powdered sugar and raspberries as desired.