In a large mixing bowl, use an electric mixer to beat 16 tablespoons of room temperature salted butter (add ¼ teaspoon kosher salt if using unsalted butter) on medium speed until smooth and creamy, about 2 minutes.
Add 2 teaspoons vanilla extract and 1 tablespoon of Instant Espresso Powder to the butter. Continue to beat until well combined.
Gradually add 3 cups of powdered sugar, one cup at a time, beating on low speed until each addition is fully incorporated. Scrape down the sides of the bowl as needed.
With the mixer on low speed, add ¼ cup cold heavy cream. Once added, increase the speed to high and beat until the buttercream is light and fluffy, about 2 minutes.
If the buttercream is too thick, you can add a little more heavy cream, one tablespoon at a time, until you reach your desired consistency. If it's too thin, add a bit more powdered sugar.
Divide the buttercream evenly over the cupcakes. Place in the freezer for 10 minutes if dipping in chocolate, just to get a bit cold.
Dip each cupcake into the chocolate, making sure to create a thin layer, the chocolate should be thin and melted, not thick.
Place in the refrigerator until set, take out and enjoy!