1. Preheat the oven to 350F. Grease a muffin tin with butter and set aside. In a large mixing bowl, use an electric mixer to beat the butter with the brown sugar until smooth. Beat in one egg at a time. Use a wooden spoon to fold in the mashed bananas. In a separate mixing bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add this mixture to the wet ingredients, mixing with the wooden spoon until incorporated. Stir in the toasted pecan pieces at the end. Divide the batter into the muffin tin, filling each space about ¾ of the way, or until all of the batter is used. Bake the muffins for about 20-25 minutes, or until cooked through. Let the muffins cool slightly.
2. While the muffins bake, heat the cream in a small saucepan over medium heat. Meanwhile, place the chocolate in a mixing bowl. When the cream comes up to a simmer, pour it into the bowl over the chocolate. Let sit for a minute or two so that the cream can melt the chocolate. Add the vanilla and stir the mixture until fully incorporated. Let cool until the ganache thickens and sets up.

To Serve

1. Spread a generous amount of chocolate ganache onto the tops of each muffin. Garnish with more toasted pecans and a sprinkle of powdered sugar.