Melt the butter in a saucepan over low heat.
Peel the bananas, cut them into small pieces and mash them to obtain a nice puree.
Add the egg, the melted butter and the milk, mixing until a very homogeneous mixture is ready.
Finally add the yeast, the flour, the vanillin and finally the brown sugar and a pinch of salt.
Mix everything together, add the chocolate chips and arrange the dough in the cups
Bake at 170 ° for about 50 minutes.