Bananas go tres tropical in this twist on a classic French upside-down tart, traditionally made with apples.
Preheat oven to 400 degrees. Roll out pastry on a lightly floured work surface to a 13 1/2-inch square. Using a large skillet as a guide, cut out a 12-inch round. Transfer pastry round to a baking sheet lined with parchment paper, and refrigerate until firm, about 15 minutes. Make three 1/2-inch slits in center of round; set pastry aside at room temperature.
Melt butter in a 12-inch skillet over medium-high heat. Stir in sugar, cinnamon, and salt. Cook, swirling skillet occasionally, until mixture turns medium amber, about 3 minutes.
Arrange bananas in skillet, overlapping slightly. Cook, without stirring, 3 minutes. Drizzle vanilla and rum over bananas, and cook until most of the rum has evaporated and liquid has thickened, about 1 1/2 minutes. Remove from heat.
Place pastry round on top of bananas, and transfer to oven. Bake until pastry is golden brown and puffed, about 25 minutes. Remove from oven, and carefully invert the tart onto a serving plate. Whisk creme fraiche until fluffy, about 3 minutes. Serve dessert warm or at room temperature with the creme fraiche.
To invert the tart, cover the skillet with a serving plate and turn over in one quick motion; slowly lift the skillet. If bananas have shifted, use a wooden spoon or spatula to move them into place.