Preheat the oven to 350-degrees. Prepare a muffin tin with liners or cooking spray.
In a large mixing bowl, sift together the dry ingredients.
In another bowl, beat the eggs until fluffy. Whisk in the butter, bananas and vanilla.
Gently mix the wet ingredients into the dry ingredients, taking care not to overmix.
Divide the batter evenly between the wells in the muffin pan.
Bake 15-20 minutes until a toothpick comes out clean. Remove from the oven and set on a wire rack to cool for 10 minutes, before removing from the pan to cool completely.
Remove the butter and the mascarpone from the refrigerator about 1 hour before preparing the frosting.
In the bowl of an electric mixer, combine the mascarpone and butter until smooth. With the mixer speed on low, add in the strawberry jam, then slowly add in the powdered sugar. You may or may not want a dash of milk depending on the consistency.