In a medium bowl, combine 3 1/2 tablespoons of the onion soup mix with 1 cup of mayonnaise and 1 cup of sour cream (or Greek yogurt).
Stir well until thoroughly blended.
Transfer your mix to a container with a tight lid, or cover your bowl with plastic wrap.
Pop it in the fridge for at least an hour, though 2-3 hours (or overnight) is ideal. This resting period allows the seasonings and creamy base to meld together.
Serve it with your favorite chips, fresh veggies, or crackers.
If you want to get fancy, sprinkle some fresh green onions, chives or parsley over the top before serving. It adds a pop of color and a little extra oniony brightness.