Russian buttercream

This is an incredibly simple buttercream with a wonderfully rich and smooth consistency. Unsalted butter is beaten until really pale, then condensed milk is slowly beaten in. As the milk is added, the texture becomes silky. The key to perfecting this is simple: make sure you beat the butter for at least 5 minutes before adding the condensed milk; it needs to be almost white. Any problems are easy to rescue. If, once you’ve added the condensed milk, the buttercream is split, that is a sign the butter was too warm. To rescue, put the bowl with the frosting into the fridge for 10 minutes and then rewhip until light and fluffy. If the butter is too cold to start with, you may find the buttercream is too dense. To correct this, take a third of the buttercream and microwave it for 10 seconds to warm slightly. Beat this back into the main bowl of buttercream.