Two kinds of chocolate—chips and cocoa powder—make this frosting extra chocolaty!
Place chocolate chips in medium microwave-safe bowl. Heat in microwave at 50 percent power for 1 minute. Use rubber spatula to stir chocolate. Return to microwave and heat at 50 percent power until melted and smooth, about 1 minute longer. Let cool slightly, about 5 minutes.
Add softened butter, sugar, cocoa powder, and salt to food processor, and lock lid into place. Turn on processor and process until smooth, about 30 seconds. Stop processor.