Make the toffee:
Fill the base pan of a double boiler (or a medium saucepan) halfway with water. Bring to a boil and then reduce heat to medium for an active simmer (just shy of a boil). Pour the sweetened condensed milk into the double boiler’s top insert (or into a stainless-steel bowl that fits snugly on top of the saucepan) and set over the simmering water. Every 45 min., check the water level in the pot and give the milk a stir. Replenish with more hot water as needed. Once the milk has thickened to the consistency of pudding and has turned a rich, dark caramel color, 2-1/2 to 3 hours, remove from the heat, cool, and cover.
Make the crust:
Meanwhile, combine the flour, 1/4 cup of the sugar, and salt in a food processor. Pulse to combine. Add the butter pieces and gently toss to lightly coat with flour. Blend the butter and flour mixture with about five 1-second pulses (count “one one-thousand” with each pulse) or until the mixture is the texture of coarse meal with some of the butter pieces the size of peas. In a small bowl, whisk together 2-1/2 Tbs. of the cream and the egg yolk and pour this over the flour mixture. Process continuously until the mixture turns golden in color and thickens in texture yet is still crumbly, about 10 seconds.
Transfer the mixture to a medium-large bowl and press the mixture together with your hand until it comes together into a ball. Shape the dough into an 8-inch-wide disk and put it in the center of an 8-1/2- to 9-inch fluted tart pan with a removable bottom. Beginning in the center of the dough and working out toward the edges, use your fingertips to gently press the dough evenly into the bottom and up the pan sides. The edges should be flush with the top edge of the pan. If you find a spot that’s especially thick, pinch away some of the dough and use it to bulk up a thin spot. Cover with plastic wrap and freeze for 1 hour.
Heat the oven to 400ºF. Right before baking, line the dough with aluminum foil and cover with pie weights or dried beans. Bake on the lower oven rack for 20 min. Carefully lift the foil (along with the weights) out of the tart pan, lower the oven temperature to 375ºF, and bake until the crust is deep golden brown, about 15 min. Transfer the tart pan to a wire rack to cool to room temperature.
Assemble the tart:
Spread the caramel over the crust using a rubber spatula or offset spatula. If the caramel has cooled and is too firm to spread easily, reheat it over simmering water in the double boiler until loosened but not hot. Slice each banana in half lengthwise and arrange the halves on top of the caramel in a circular pattern. To fit the banana halves snugly in the center of the pan, cut them into smaller lengths.
Put the coffee granules in a small zip-top bag. Press a rolling pin back and forth over the granules to crush them into a powder.
In a chilled medium stainless-steel mixing bowl, beat the remaining heavy cream, the vanilla, and the remaining 2 tsp. sugar with an electric mixer at medium-high speed until it holds soft peaks when the beaters are lifted. Spoon the whipped cream over the bananas, sprinkle with the coffee powder, remove the pan sides, and serve.
Make Ahead Tips
The caramel can be made up to three days ahead, covered tightly and refrigerated. The crust can be baked up to a day ahead, then wrapped tightly in plastic wrap. The finished tart can be held for 30 minutes in the refrigerator, though it's best not to sprinkle on the coffee powder until just before serving.
nutrition information (per serving):
Photo: Scott Phillips