To test whether the mixture – or crème anglaise – is done, dip a spoon in the mixture and run your finger through the custard down the back of the spoon. If the path you’ve just created with your finger holds its shape, the custard is done. If you are unsure about this step, you can use a sugar thermometer. The crème anglaise is done once the mixture reaches a temperature of 80°C (175°F).