4 ounces (½ package) cream cheese (Philadelphia, or supermarket brand)
4 tbsp (½ stick) butter
¼ cup unsweetened cocoa powder, or extra to taste.
2 cups confectioners (US: powdered; UK: icing) sugar (about ½ a 1lb box)
½ tsp vanilla extract
Bring cream cheese and butter to room temperature.
Cream with vanilla extract in mixer or food processor.
Add cocoa powder & sugar 1 cup at a time, blending at low speed until incorporated.
Taste for balance; I used Nestlé cocoa and found it needed a couple of teaspoons extra to round out the chocolate flavour.
Blend on medium speed 1 minute until fluffy.
(From Anne Byrn’s The Cake Mix Doctor.)