Beat the butter with sugar until foamy, mix in the eggs one by one, keep stirring and add the oil.
Finely mash the bananas, mix with lemon juice. Sift the flour with baking powder, add to the dough with the bananas, stir everything briefly. Pour the batter into muffin cups. Melt butter in a small pan, add maple syrup and nuts, let simmer for approx. 2 minutes so that some liquid evaporates, but don`t burn.
Spread on the muffins. Bake muffins at 170 degrees (fan oven) or 180 degrees (top-bottom heat) for 25 - 30 minutes.