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1
Preheat oven to 325F.
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2
Line a standard muffin tin with paper liners.
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3
Whisk together flour, baking powder, and salt.
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4
Put butter and chocolates in a heatproof bowl set over (not in) a pan of simmering water; stir until melted.
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5
Remove from heat, and let cool slightly.
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6
Whisk granulated sugar into cooled chocolate mixture.
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7
Add eggs, and whisk until mixture is smooth.
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8
Stir in vanilla.
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9
Add flour mixture; stir until well incorporated.
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10
Spoon 2 tablespoons chocolate batter into each lined cup, followed by 1 tablespoon peanut butter filling.
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11
Repeat with another tablespoon of batter, and top with 1 teaspoon filling.
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12
Swirl top of cupcake batter and filling with a wooden skewer or toothpick.
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13
Bake, rotating tin halfway through, until a cake tester inserted in centers comes out with only a few moist crumbs attached, about 40 minutes.
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14
Transfer tin to a wire rack to cool completely before removing cupcakes.
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15
Cupcakes can be stored up to 3 days at room temperature in airtight containers.
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16
Stir together all ingredients until smooth.
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17
Use immediately.
