Marinated pepperoncini peppers, tender and perfectly spicy, add a nice heat and punch of flavour to the mayonnaise. If you prefer a spicier mayonnaise, keep some or all of the seeds from the peppers.
By combining the milk, sour cream and white vinegar, you are essentially preparing a homemade buttermilk, which will give you a texture and acidity similar to that of store-bought buttermilk.