Use any oil you like best. I like rape seed oil, I fry with it, bake with it and use it in salad dressings and when I make mayonnaise. It is mild and supports other flavours brilliantly.
Grind together garlic, mustard powder, salt and pepper. Add lemon juice, tarragon vinegar and honey. Mix. Will keep in fridge for 14 days.
Shake before adding to your salad or cold leftover boiled veggies such as beans, carrots , peas and so on.