Cornish Fish Stew

For stew

• 2 tablespoons butter or olive oil
• 1 medium onion diced
• 1 leek white and light green parts only, sliced
• 2 celery stalks sliced
• 2 cloves garlic minced
• 1 pound Yukon Gold or russet potatoes, peeled and cut into 1-inch chunks
• 1 (14.5-ounce) can diced tomatoes
• 3 cups fish broth or chicken broth
• 1 bay leaf
• 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
• 1 teaspoon salt plus more to taste
• 1/2 teaspoon black pepper
• 1 1/4 pounds firm white fish fillets cut into large chunks, (cod, haddock, pollock, or halibut)
• 1/2 pound mussels or peeled shrimp, (optional)
• 1/2 cup heavy cream or half-and-half, (optional, for a richer stew)
• 2 tablespoons fresh parsley chopped
• 1 tablespoon lemon juice
• Crusty bread For serving
• extra parsley For serving
• Lemon wedges For serving