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1
Position a rack in the center of the oven and preheat to 350 degrees F. Butter and flour a 9-by-5-by-3-inch loaf pan.
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2
Put the chocolate in a heatproof bowl.
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3
Bring a saucepan filled with an inch or so of water to a very slow simmer; set the bowl on the pan (without touching the water).
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4
Stir occasionally until melted and smooth.
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5
Keep warm.
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6
Whisk the flour, baking soda, baking powder, cinnamon, and cloves in a medium bowl.
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7
Stir the vanilla and half the bananas into the buttermilk.
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8
Beat the butter and sugar in a large bowl, with an electric mixer on medium-high speed until light and fluffy, about 4 minutes.
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9
While mixing, drizzle in the oil and beat until incorporated.
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10
Beat in the egg.
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11
While mixing slowly add the flour mixture to the butter in 3 additions, alternating with the buttermilk mixture in 2 parts, beginning and ending with the flour.
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12
(Scrape the sides of the bowl between additions, if needed).
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13
Fold in the remaining bananas.
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14
Gently swirl the melted chocolate into the batter so that it has a marbled effect.
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15
Scoop the batter into the prepared pan.
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16
Bake until a toothpick inserted in the center comes out clean, about 50 minutes.
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17
Cool in the pan on a rack before unmolding and slicing.
