Mash the remaining bananas with the strained lemon juice to a purée. Whisk the single cream and double cream together until thick, then fold in the almost set jelly and the mashed bananas. Pour into the mould over the decorative base. Leave in a cool place until set firm. Loosen round the top edges of the mould and dip for a moment into water – as hot as the hand can bear. Place a serving plate over the top and invert the mould on to it, giving a good sharp shake so that the dessert slides out. Serve with pouring cream.