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1
Make the custard In a medium saucepan, combine the milk with the vanilla extract and banana and bring to a simmer.
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2
Remove from the heat and let stand at room temperature for 1 hour (or refrigerate overnight).
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3
Return the mixture to a simmer, then strain through a sieve into a heatproof measuring cup; discard any solids.
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4
Make the custard In a large bowl, combine the egg, egg yolk, sugar, cornstarch and salt and whisk until thickened and smooth.
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5
While whisking constantly, gradually whisk in 1/4 cup of the hot milk to temper the eggs, then gradually whisk in the remaining milk until combined.
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6
Make the custard Pour the egg-and-milk mixture into the saucepan and cook the custard over low heat, whisking constantly, until thickened, about 8 minutes.
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7
Strain the custard through a sieve into a bowl.
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8
Press a piece of plastic wrap directly on the surface of the custard and refrigerate until chilled, at least 1 hour.
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9
Meanwhile, make the cupcakes Preheat the oven to 350 and line a 12-cup muffin tin with paper liners.
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10
In a medium bowl, whisk the flour with the baking powder and salt.
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11
Meanwhile, make the cupcakes In a large bowl, using a handheld electric mixer, beat the butter with the peanut butter, granulated sugar and brown sugar at medium-high speed until fluffy, about 3 minutes.
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12
Beat in the eggs, one at a time, then beat in the vanilla.
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13
At low speed, beat in half the flour mixture, then all the milk, followed by the remaining flour mixture.
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14
Meanwhile, make the cupcakes Fill the prepared muffin cups with the batter until almost full and bake for about 20 minutes, until a toothpick inserted in the center of the cupcakes comes out clean.
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15
Transfer the cakes to a wire rack and let cool completely.
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16
Make the frosting Put the peanut butter chips in a large heatproof bowl.
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17
In a small saucepan, bring the heavy cream to a simmer, then pour it over the peanut butter chips and let stand for 5 minutes.
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18
Add a pinch of salt and whisk the frosting until smooth; let cool, stirring occasionally, until spreadable.
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19
Make the frosting Transfer the banana cream into a piping bag fitted with a large round tip.
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20
Insert the tip into the top of each cupcake and fill with some of the cream.
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21
Frost the cupcakes and garnish with peanuts.
