In a 12-inch non stick skillet, heat two tablespoons of the butter over medium heat.
Add the mushrooms and cook until liquid is released and they are golden brown.
Stir in the Dijon mustard and Worcestershire sauce. Cook for a minute or two. Remove the mushrooms to a clean bowl.
Heat the remaining two tablespoons of butter in the same pan. Add the chopped shallots and minced garlic. Cook for 1-2 minutes, until fragrant.
Add the rice and stir to coat with the butter. Add 3/4 cup of the wine. Stir occasionally until the wine is almost all absorbed. Reduce the heat to medium low.
Add three cups of the chicken stock or broth. Give it a good stir. Stir every 5 minutes or so, until most of the broth is absorbed.
Add the remaining 1/4 cup of wine and 1 cup of chicken broth. Again stir occasionally until much of the liquid is absorbed.
Taste the rice to be sure it is cooked through. It should be creamy and the liquid should have formed a thick sauce by now.
Stir in the cooked chicken and mushroom. Then add the Parmesan and Brie. Stir well and continue to cook until it the risotto is warmed through.
Garnish the risotto with more Parmesan and fresh thyme and serve.