How do you fix curdling?

If a dairy-based sauce curdles, immediately halt the cooking process. Take your pan off the heat and place it in an ice bath. If the clumps are relatively few, you can pour the whole sauce through a sieve. Whisk the strained sauce vigorously to break up any tiny remaining lumps. Proteins are more likely to bond with each other when there are a lot of similar molecules in a small space, so one way to discourage their fraternization is to introduce some different molecules, such as starch or fat. So make a roux and slowly whisk in the curdled sauce, or heat a hefty splash of full-fat milk or cream in a saucepan and add it to the pan.