2 tablespoons unsalted butter
2 Vidalia onions, sliced into 1/4-inch-thick rings
2 large shallots, sliced into 1/8-inch-thick rings
3 cloves garlic, minced
2 cups sour cream
1 cup mayonnaise
1 teaspoon celery salt
1 teaspoon Worcestershire sauce
Kosher salt and freshly ground pepper
Chives, finely chopped, for garnish
Potato chips, for serving