¼teaspoonmustard powder (optional)or use ½ teaspoon Dijon mustard
Instructions
Add the yogurt, cornflour, egg, seasoning and lemon juice to a pan and whisk to mix all the ingredients together.
Place the pan on a very low heat. Bring to a simmer, whisking constantly. As soon as the sauce reaches a simmer, remove from the heat.
Add the butter and whisk until melted. You should have a smooth silky sauce.
Notes
If you prefer, you can use 2 egg yolks rather than a whole egg. The sauce will be a little richer and darker yellow.Note that cornflour is also known as cornstarch in some countries. It is a fine white powder.Seasonings: use white pepper if you don't want visible dark flecks of pepper. You can also add optional seasoning such as a pinch of cayenne or paprika instead of mustard.