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1
Preheat the oven to 350F.
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2
Butter two 9-by-2-inch round cake pans; line bottoms with parchment.
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3
Butter parchment and dust with flour, tapping out excess; set aside.
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4
Into a medium bowl, sift together flour, baking powder, baking soda, and salt.
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5
In a small bowl, stir together mashed bananas, sour cream, and vanilla; set aside.
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6
In the bowl of an electric mixer fitted with the paddle attachment, beat 1 1/2 sticks butter and 1 2/3 cups sugar on medium-high speed until light and fluffy, 3 to 4 minutes, scraping down the sides of the bowl as needed.
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7
Add the eggs, one at a time, beating well after each addition.
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8
With mixer on low speed, add the flour mixture in two parts, beating until combined after each, 2 to 3 minutes.
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9
Using a rubber spatula, fold in the reserved banana mixture, being careful not to overmix.
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10
Divide the batter between the prepared pans.
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11
Bake, rotating the pans halfway through, until cakes are golden brown and a cake tester inserted in the centers comes out clean, 30 to 35 minutes.
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12
Transfer pans to a wire rack to cool 20 minutes.
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13
Invert cakes onto the rack; peel off the parchment.
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14
Reinvert cakes, and let them cool completely, top sides up.
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15
Sprinkle remaining 1/4 cup sugar into a large skillet; cook over high heat, shaking the pan occasionally, until sugar is caramelized.
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16
Remove from heat; stir in remaining 3 tablespoons butter until melted.
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17
Return pan to medium heat.
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18
Add the sliced bananas; cook until slices start to brown, 1 to 2 minutes.
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19
Gently turn the bananas, and cook over medium-high heat until browned, about 2 minutes more.
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20
Using a serrated knife, trim tops of layers to make level.
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21
Place one layer on a cake plate; arrange caramelized banana slices on top.
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22
Place remaining layer on top.
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23
Using a large offset spatula, spread Mascarpone Frosting over entire cake, swirling to completely cover.
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24
Drizzle Caramel Sauce over the top of the cake, or serve some alongside each slice.
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25
Serve immediately, or refrigerate, covered with a cake dome, for up to 3 days.
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26
In the bowl of an electric mixer fitted with the paddle attachment, beat the mascarpone, cream, and confectioners sugar until medium-soft peaks form, 1 to 2 minutes.
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27
Be careful not to overbeat.
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28
Use immediately.
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29
Prepare an ice bath; set aside.
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30
Cook sugar in a medium saucepan over medium-high heat until it starts to melt around edges; then shake pan to melt remaining sugar.
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31
Continue to cook, stirring with a wooden spoon, until golden amber, about 3 minutes.
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32
Remove from heat.
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33
Stirring constantly, add cream in a slow, steady stream (it will spatter).
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34
If necessary, return pan to heat for a few seconds, stirring until mixture is smooth.
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35
Place caramel in a bowl in the ice bath; let stand until cold, stirring frequently.
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36
Long slices of banana are added to a skillet of caramel, then browned on both sides.
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37
The caramelized bananas are arranged on the bottom layer of banana cake, then covered with the top layer of cake.
