Spread defrosted pastry sheet on a baking sheet. Bake 10 minute or until golden. Remove from baking sheet and cool on wire rack.
Slice bananas into 1/4" discs.
Combine 1/2 cup brown sugar, rum, butter, lemon juice and cinnamon in skillet over low heat. Bring mixture to a boil. Cook and stir until thickened, about 2 minute. Remove from heat, then add bananas and toss to coat.
Mix sour cream and remaining brown sugar. Spoon banana mixture over cooled pastry. Top with sour cream mixture. Cut into wedges and serve.