You really can't mess up this recipe for Foolproof Chocolate Frosting. As long as you follow the instructions, it's perfect every time!
In food processor, process butter, sugar, cocoa, and salt until smooth, about 30 seconds, scraping sides of bowl as needed. Add corn syrup and vanilla and process until just combined, 5 to 10 seconds. Scrape sides of bowl, then add chocolate and pulse until smooth and creamy, 10 to 15 seconds. Frosting can be used immediately or held. Makes 3 cups to frost one 9-inch 2-layer cake. NOTE: This frosting may be made with milk, semisweet, or bittersweet chocolate