Sift the flour, cocoa powder, baking soda, and salt into the bowl. Whisk until the ingredients come together in a smooth batter.

Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

Bake the cupcakes on middle rack of oven until a toothpick inserted in the center comes out clean, 18-21 minutes.

Check to see that cupcakes are done. Remove from oven or add time as needed.

Allow the cupcakes to cool completely to room temperature before frosting.

While the cupcakes cool, make the frosting. Place the butter in a large mixing bowl and beat with a hand mixer on medium speed until smooth and creamy.

Add half the powdered sugar and cocoa powder to the bowl with the butter, beating on low speed until mostly incorporated. Add the remaining powdered sugar and cocoa, the vanilla extract, heavy cream, and salt to the bowl. Continue beating on medium-high speed until the frosting is light and fluffy, 2-3 minutes. Add more heavy cream as needed to reach the desired consistency.

Pipe or spread frosting onto the cooled cupcakes. Refrigerate until ready to serve.