1 cup all-purpose flour
1 teaspoon baking powder
1⁄2 teaspoon salt
6 tablespoons (3⁄4 stick) unsalted butter, softened
3⁄4 cup creamy peanut butter (regular, not natural)
1⁄2 cup packed light brown sugar
1⁄4 cup granulated sugar
1 large egg
2 teaspoons pure vanilla extract
1⁄2 cup whole milk
Chocolate Frosting (see below)
Fleur de sel or chopped salted peanuts for sprinkling (optional)
4 ounces bittersweet chocolate, chopped
1⁄2 cup heavy cream
3 tablespoons unsalted butter
1 tablespoon light corn syrup
1⁄4 teaspoon fine sea salt
1. Put the chocolate in a medium-size heatproof bowl and set aside.
2. Combine the cream, butter, corn syrup, and salt in a small saucepan and heat over medium heat until very hot but not boiling, about 4 minutes.
3. Quickly pour the hot cream mixture over the chopped chocolate. Let stand for 5 to 7 minutes to melt the chocolate, then whisk until smooth. Refrigerate for 30 minutes, then beat with an electric mixer until light and fluffy. The frosting will keep for up to 3 days, refrigerated, in an airtight container. Bring to room temperature before using.
1. Preheat the oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
2. Sift the flour, baking powder, and salt together into a medium-size bowl.
3. In the bowl of a stand mixer fitted with a paddle attachment, beat the butter, peanut butter, brown sugar, and granulated sugar together on medium speed until light-colored and creamy, about 1 minute.
4. Beat in the egg for 30 seconds. Scrape down the sides of the bowl, then mix in the vanilla and beat on medium speed for 1 minute. Scrape down the sides of the bowl again.
5. Add the flour mixture in 3 increments, alternating with the milk (which you’ll add in 2 increments), beginning and ending with the flour mixture and beating after each addition. Mix until just combined.
6. Fill each cupcake liner three-quarters full with batter. Bake for about 20 minutes, until the tops of the cupcakes are golden and firm and a cake tester comes out clean. Let cool in the pan on a wire rack for 15 minutes, then transfer the cupcakes to a wire rack to cool completely before frosting. When cool, frost each cupcake with chocolate frosting. Sprinkle lightly with either fleur de sel or chopped salted peanuts, if desired. The frosted cupcakes will keep, covered, at room temperature for up to 2 days.