Chicken Fricassee

2 pounds boneless - skinless chicken thighs
8 ounces portobello mushrooms sliced
1 onion chopped
2 garlic cloves minced
2 celery stalks diced
1 carrot diced
3 cups chicken stock
1/2 cup sherry
1/2 cup heavy cream
2 tablespoons flour
1 teaspoon fresh thyme
2 tablespoons fresh tarragon 
1 tablespoon chopped parsley
2 tablespoons olive oil divided
1 tablespoon butter (optional)
2 tablespoons fresh squeezed lemon juice
2 teaspoons kosher salt
1/2 teaspoon fresh ground pepper

In a large skillet, use 1 Tbsp. oil brown to the chicken on both sides 
5 minutes each.
Transfer the chicken to a platter.
Pour off all the fat that has rendered from the chicken. Then use 
reaming oil to Sautée the onions, celery & carrot until softened.
Add the mushrooms, thyme & brown about 5 minutes. Then add the garlic & 
cook for 30 seconds.
Stir in the flour & let cook for 1 minute.
Whisk in the sherry to deglaze the pan. Be sure to scrape up all bits 
on the bottom of the pan. Then add the stock & bring to a boil. Reduce 
to a simmer & add back the chicken. Simmer partially covered for 20 
minutes. Add the tarragon, lemon, cream and let simmer 2 minutes
Stir in the optional butter to "gloss" the sauce. However in my kitchen 
this is not optional!