Vidalia Restaurant Caramelized Vidalia Onions

Source: Chef Jeffrey Buben - Vidalia Restaurant, Washington, DC

4 jumbo Vidalia onions, whole

Filling
8 tablespoons unsalted butter, softened
1/4 cup light brown sugar
1 tablespoon chopped garlic
2 tablespoons chopped shallots
1/4 cup sherry vinegar
1/4 cup beef or chicken stock
4 teaspoons fresh rosemary, stemmed and chopped
4 teaspoons fresh thyme, stemmed and chopped
2 tablespoons olive oil
4 shiitake mushrooms, stemmed and diced finely

Preheat the oven to 350 degrees F.

Prepare the onions: Keeping the outer layers on the onions, remove the stem and using a paring knife, make 6 vertical cuts around the onion, 2 layers deep, and pull down the 6 sections forming a crown on top.

In a bowl, mix the filling ingredients except for the mushrooms. Divide the filling ingredients in the center of four 12-inch-by-12-inch pieces of aluminum foil.

Hold the crown of each onion and place on top of the filling ingredients. Draw the squares of aluminum foil from 4 corners to the top center like a pyramid with the crown sticking out. Seal well by pressing in the foil.

Place the onions on a sheet pan and bake in the oven for about 1 hour and 10 minutes, or until soft.

Make the sauce: In a small, hot skillet, heat the olive oil and saut