Instructions

• Preheat oven to 350°F. Line a 12-cup muffin pan with cupcake liners and set aside.
• Place 1 cup (2 sticks) unsalted butter and 8 ounces chopped dark chocolate in a heatproof bowl. Set the bowl over a saucepan of gently simmering water (the bottom of the bowl should not touch the water). Stir occasionally until the butter and chocolate are completely melted and smooth. Remove the bowl from the heat.
• Whisk the melted chocolate mixture until smooth, then whisk in 1 cup packed light brown sugar, 1 teaspoon instant espresso powder (if using), and 2 teaspoons pure vanilla extract. Let the mixture cool for a few minutes so it is warm but not hot.
• Add the 4 large eggs plus 1 egg yolk (all at room temperature) to the chocolate mixture one at a time, beating or whisking well after each addition until fully incorporated.
• Whisk in 1 cup all-purpose flour (do not pack the flour), 1/2 teaspoon salt, and 1/4 teaspoon baking powder. Mix just until combined—do not overmix.
• Fold in 1/2 cup bittersweet chocolate chips until evenly distributed.
• Divide the batter evenly among the prepared cupcake liners (about 3/4 full for each liner).
• Bake for 21–25 minutes, or until a wooden pick inserted into the center of a cupcake comes out with a few moist crumbs (centers will be fudgy). Remove the pan from the oven and let the cupcakes cool in the pan for 20 minutes.
• After 20 minutes, transfer the cupcakes to a wire rack and let them cool completely before frosting.
• While the cupcakes cool, make the salted caramel frosting: in a medium saucepan over medium heat combine 1/2 cup (1 stick) unsalted butter, 1/2 cup heavy cream, 2 teaspoons pure vanilla extract, 1 cup packed light brown sugar, and 1/2 teaspoon salt. Cook, stirring occasionally, until the sugar is melted and the mixture comes to a low simmer, about 4 minutes.
• Remove the saucepan from the heat and let the caramel mixture cool for 2 minutes.
• Pour the warm caramel mixture into the bowl of an electric mixer fitted with the whisk attachment. Add 2 cups sifted confectioners’ sugar and beat on medium-low speed until incorporated.
• Add the remaining 1 cup sifted confectioners’ sugar (for a total of 3 cups) and increase the mixer speed to medium-high. Beat until the frosting is thick and fluffy, about 4–6 minutes.
• If needed, scrape down the bowl and beat briefly again to ensure an even texture. Frost the cooled cupcakes with the salted caramel frosting as desired.