Seared Salmon with Onions and Rhubarb

Name: Seared Salmon with Onions and Rhubarb
Ingredients: 1 1/2 cups dry fino sherry; 1/4 cup turbinado sugar or palm sugar (See Note); 1/2 pound rhubarb, trimmed and sliced diagonally 1/3 inch thick; 3 tablespoons unsalted butter; 1 pound bulb onions or sweet white onions, thinly sliced; 1/2 cup chicken stock or canned low-sodium broth; 1 thyme sprig; Salt and freshly ground pepper; 1 pound fava beans, shelled; Four 6-ounce salmon fillets, skin on; Vegetable oil; 1 teaspoon fresh lemon juice