[header] How to make rainbow cupcakes with rainbow frosting [title] Preheat the oven to 350 degrees fahrenheit or 176 degrees celsius. [title] Place 24 cupcake liners onto a cupcake tray. [title] In a large bowl, cream the butter and sugar until light and fluffy. 
[step] Beat for about 2-3 minutes. [title] Pour in the vanilla extract and egg whites.