Whisk the mustard and vinegars together in a non-reactive bowl.
Slowly drizzle the oils into the mixture, continuing to whisk to emulsify.
Taste and season as desired.
Note: a standard formula for vinaigrettes is 1 Part Vinegar: 3 Parts oil.
Note on Salad Dressings and Vinaigrettes
This recipe is my “home” dressing, to keep on hand but you can substitute any number of items such as flavoured oils, vinegars, seasonings and herbs to suit your personal preferences.