In a large saute pan, heat the butter over medium-high heat. Add the onions and saute, stirring occasionally, for 15 to 20 minutes, or until golden brown and caramelized. Add the shallots and saute for 8 to 10 more minutes, until the onions and shallots are dark brown. Add the garlic and saute for 2 minutes. Remove from the heat and let cool for
5 minutes, then chop into 1/4-inch pieces. Set aside to cool to room temperature.
In a bowl, mix the sour cream, mayonnaise, celery salt, Worcestershire sauce and 1 teaspoon each salt and pepper. Fold in the onion mixture. Refrigerate at least 1 hour or overnight. Garnish with chives and serve with potato chips.