Could not find any copycat recipe. But did find this recipe you could experiment with. Please share your results with us.

MARC MEYER'S FRESH HORSERADISH
AND ROASTED ONION DIP

1 small (or 1/2 medium-large) horseradish root, peeled and diced
1/4 cup white vinegar
Salt and pepper to taste
Olive oil
2 medium white onions, sliced
1 cup creme fraîche
1 teaspoon chopped fresh tarragon

Add horseradish, vinegar, and a pinch of salt to a food processor, and pulse until smooth, but not pureed. Reserve.

Heat one tablespoon olive oil in a medium saucepan and add sliced onions. Cook over low flame until very soft, about 45 minutes. Let cool.

In food processor, pulse onions with pinch of salt and pepper until almost a purée. Remove from processor.

Using a spatula, remove onion mixture from processor and combine with horseradish and creme fraîche until smooth. Fold in fresh tarragon.

Serve with bread or breadsticks.

Source: New York Times Recipes, January 23,2006