After tons of testing and tweaking, I've finally discovered the BEST Chocolate Cupcake recipe! Truly! Keep reading for lots of recipe tips, insights into the science of baking, and the full printable recipe.
In a medium heatproof bowl, combine the chocolate, cocoa powder, and espresso powder. Pour hot water over mixture. Cover and let stand for 5 minutes. Whisk mixture gently until smooth, then set aside to cool.
In a small bowl, whisk together the flour, sugars, salt, and baking soda.
Whisk sour cream, oil, eggs, egg yolk, vinegar, and vanilla into the cooled chocolate mixture until smooth, scraping down the sides and bottom of the bowl as you mix. Stir in the flour mixture until smooth, being careful not to overmix.
Using a spring-loaded scoop, divide the batter evenly among prepared muffin cups until 3/4 full. Bake until cupcakes are set and firm to the touch, about 17 to 18 minutes.
Let cupcakes cool in pan on a wire rack for 10 minutes before removing from pan to cool completely, about 1 hour. Cupcakes can be stored in an airtight container at room temperature for up to 1 day.
Make the frosting:
In a small saucepan, bring the cream to a simmer. Remove from heat and add the chopped chocolate. Let stand for a few minutes before stirring until smooth. Set aside and cool to approximately 75°F or until thickened but still pourable.
In the bowl of a stand mixer fitted with the paddle attachment, add the butter, powdered sugar, cocoa, vanilla, and salt. Mix on low speed until well blended and then increase the speed to medium and beat for another 3 minutes, or until very well blended, scraping down the bowl as needed.
Reduce speed to medium-low and add the cooled chocolate cream mixture. Continue beating until the frosting has lightened in color and texture, about 2 minutes more, scraping down the bowl as needed.
Frosting can be made 1 day ahead of time and stored in an airtight container in the refrigerator. Warm frosting in the microwave for 5 to 10 seconds and stir until creamy again before frosting cupcakes.
Frosting can also be transferred to a ziptop bag and frozen for up to 1 month. Defrost in the fridge overnight then rewhip in the stand mixer until light and smooth.
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Notes
Cupcake yield will depend on the size of your muffin tin cavities. If they’re smaller, you may need two pans to make 15 total cupcakes. You can use 1/2 cup hot strongly brewed coffee in place of the espresso powder + hot water. If using natural cocoa powder, omit the vinegar. For the frosting, opt for organic powdered sugar made with tapioca starch, such as Wholesome, instead of cornstarch, for a smoother silkier texture.