Ingredients for 1 cupful :

• 1 tablespoonful (tbsp) neutral vegetable oil, e.g. sunflower
• pinch of sugar
• pinch of black ground pepper
• half a level teaspoonful (tsp) mild mustard
• 1 level tsp bouillon powder or concentrated liquid bouillon (or crushed bouillon cube); if bouillon is unsalted, add salt to taste.
• 1 level tsp finely chopped onion
• half a clove of garlic, crushed
• fresh or dried dill, finely chopped
• (1 tsp finely chopped chives or parsley if liked)
• pinch of fresh or dried tarragon
• three-quarters cup plain full-cream yoghurt
• white balsamic vinegar to taste

Method :

 Homogenize the ingredients in a blender.

This sauce keeps at least a week in a screw-topped jar in the refrigerator. If it is too thick, add a little milk.