Instructions

• Preheat the oven to 350°F (177°C). Line a cupcake pan with paper liners and set aside.
• In the bowl of a stand mixer, combine 1 3/4 cups cake flour, 1 1/4 cups all-purpose flour, 1 3/4 cups granulated sugar, 2 1/2 teaspoons baking powder, and 1 teaspoon kosher salt. Mix on low speed for 1 minute to blend.
• With the mixer on low, add 1 cup (227 g) unsalted butter, cut into 1/2-inch cubes, a few pieces at a time. Continue mixing on low until the mixture resembles coarse sand.
• Keeping the mixer on low, add the 4 eggs one at a time, scraping down the sides of the bowl after each addition. With the mixer still on low, slowly pour in 1 cup (244 ml) whole milk and 2 teaspoons vanilla extract and mix just until combined.
• Increase the mixer speed to medium and beat the batter for 2 minutes, until smooth. Scrape the sides and bottom of the bowl as needed to ensure everything is incorporated.
• Fill the prepared liners about two-thirds full (about 1/4 cup of batter per liner). Bake at 350°F for 15–20 minutes, until the centers are set and a toothpick inserted into the center comes out clean.
• Cool the cupcakes in the pan for 10 minutes, then transfer them to a wire rack to cool completely before frosting.
• While cupcakes cool, melt 8 ounces (226.8 g) semisweet chocolate and let it cool to room temperature (use a microwave in short bursts, stirring between bursts, or a double boiler).
• Make the frosting: in the stand mixer fitted with the wire whisk attachment, whip 2 cups (454 g) unsalted butter on medium-high speed for 5 minutes, stopping once or twice to scrape the bowl.
• Reduce the mixer speed to low and gradually add 5 cups (600 g) powdered sugar until incorporated. Increase the speed to medium-high, add 2 teaspoons vanilla extract, and mix until combined.
• Add the cooled melted chocolate to the buttercream and whip at medium-high speed until the frosting is light and fluffy, about 2 minutes, scraping the bowl as needed to fully incorporate the chocolate.
• Frost the cooled cupcakes as desired. Store frosted cupcakes in an airtight container at room temperature for up to 3 days. Unused buttercream can be refrigerated in an airtight container for up to 3 days; bring it to room temperature and briefly rewhip before using.