Chicken in Cream Sauce Volaille a La Crème

Name: Chicken in Cream Sauce (Volaille a La Crème)
Ingredients: 5 tablespoons butter; 4 lbs chicken, cut into 8 pieces; 3⁄4 teaspoon salt; 1⁄4 teaspoon ground black pepper; 1 1⁄4 cups white pearl onions, peeled; 1 cup white mushroom, cleaned with bottoms trimmed; 1 shallot, thinly sliced; 1 teaspoon granulated sugar; 1 cup dry white wine; 1⁄2 cup chicken stock; 1 sprig fresh thyme; 2 cups creme fraiche (can sub sour cream)