Charred Onion Dip

From: Chef Kevin Johnson, The Grocery, Charleston, S.C.

5 lb. onions, very thinly sliced
12 sprigs thyme, picked and minced
6 oz. butter
splash of olive oil
to taste, salt and pepper
1 cup buttermilk, plus more if needed
2 cups sour cream
1 cup mayonnaise
¼ to ½ cup sherry vinegar

Mix onions with butter, olive oil and thyme. Caramelize onions slowly in wood oven until deep, dark brown. Puree onions in food processor with buttermilk once they have cooled. Add sour cream, mayonnaise and sherry vinegar. Puree until very smooth. Add more buttermilk if needed. Adjust acidity with more vinegar. Season with salt and pepper.