Cream together the butter and sugar.
Beat the eggs and stir into the mixture.
Mash the bananas, then combine into the mixture until smooth.
Gradually fold in the flour and baking soda until the batter is thick and sticky.
Spoon the batter into lined muffin tins or a greased loaf pan and bake at 190C/375F for 20 minutes for muffins, 50-60 minutes for a loaf.