In a saucepan combine 3 bananas, peeled and sliced, with 1/4 cup water and the sugar and simmer the mixture for 15 minutes, skimming off the foam that rises to the top.
Force the mixture through a fine sieve or puree it in a blender.
Stir in sour cream and rum. Line 6 tart pans with sweet tart pastry and prick the pastry well with a fork.
Line the shells with wax paper and fill them with rice.
Bake the shells in a moderate oven (350° F) for about 15 minutes, or until they are golden brown.
Discard the rice and paper. Remove the shells from the pans and, while they are still warm, fill them with the banana cream.
Garnish each tart with pitted dark sweet cherries.