Make frosting by beating together butter, lemon juice and salt until light and fluffy, about 1 minute.
Mix in ¼ cup heavy cream, cocoa powder and 1 cup powdered sugar and combine.
Slowly add in the rest of the powdered sugar ½ cup at a time until all 3 cups have been incorporated.
Turn your stand mixer on high and beat for the next 5 minutes until light and fluffy.
Frost cake. Store any extra frosting in the refrigerator.
The calories shown are based on the recipe making about 2 cups of frosting, with 1 serving being 3 tablespoons of frosting. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information.**