Melt butter and olive oil in a large skillet
Place chicken bone-side up in the skillet, and brown, turn and brown the other side and remove the chicken, leaving the fat and juices in the skillet. Place chicken in a bowl
Add onions and stir gently until browned
Add minced garlic and stir for about 10 seconds
Pour in the sherry and deglaze the pan making sure to release the brown bits from the bottom and sides of the skillet
Move onions and garlic to the sides and add the chicken back into the skillet along with any juices in the bowl
Add the rutabaga, carrots, and parsnips and scatter around the chicken and onions
Mix 2 cups chicken stock, Dijon mustard, and lemon juice and pour over chicken and veggies
Add the cover back to the skillet and simmer for about 20 minutes or until the chicken is cooked
Arrange chicken and veggies on plates that can hold some of the broth. Pour a little stock from the pan over top.
Garnish with grated lemon peel and parsley. Serve with slices of warm, thick-cut pumpernickel bread to sop up the juices