Why did your potato gratin curdle?

Potato gratin should not curdle. If you are referring to a recipe that resulted in a curdled dish, it is likely that the cause was either excessive heat or the use of an acidic ingredient, such as lemon juice or wine, that caused the milk or cream to curdle. To prevent curdling, ensure the oven temperature is correct and stir the gratin regularly. Additionally, avoid using acidic ingredients or reduce their quantity.