Line the muffin tin with paper liners or grease with butter or oil. Preheat the oven to 170 ° C convection or 190 ° top and bottom heat.
Beat the butter and sugar with a mixer until frothy. Stir in the eggs one at a time. Add vanilla extract and mix well. Mix the flour, baking powder, lemon zest and salt. In a small bowl, crush the bananas with a fork.
Add the flour mixture to the butter-egg mixture alternately with the banana and stir.
Fill the tins about 2/3 high with batter. Bake for about 30 minutes. Make a chopstick test.
The muffins are very juicy and very soft. They hold up very well and are still very juicy after 5 days. You can also freeze them and, when in use, let them thaw and put them in the hot oven for 5 minutes.