Salmon, sweet potato, and broccoli chowder

1 large onion, chopped (2 cups)
3 T unsalted butter
¼ c all purpose flour
3 c chicken broth
2 cups whole milk
1 large sweet potato, peeled and diced (1 ½ c)
1 bay leaf
1 t fresh thyme leaves
1 pound skinless salmon fillet
1 small broccoli stalk, cut into pieces ( ½ cup)
¼ t kosher salt

In a large, heavy saucepan, over medium heat, cook the onion in the butter until softened, about five minutes. Add the flour and stir until smooth. Whisk in the broth and milk, then add the sweet potatoes, bay leaf, and thyme. Bring to a boil, reduce heat, and simmer. Stirring occasionally, eight minutes. Add the fish or meat and broccoli; simmer five minutes for the salmon, seven minutes for the chicken or ten minutes for the pork. Season with the salt and pepper.