Slow-Cooker Shrimp & Crab Bisque

Name: Slow-Cooker Shrimp & Crab Bisque
Cuisine: European, American
Ingredients: 1 tablespoon olive oil; 2 tablespoons butter; 3 leeks, washed well and sliced; 4 garlic cloves, minced; Pinch of red pepper flakes; 2 tablespoons tomato paste; 4 cups seafood or fish stock; 2 cups water; 1 (15-oz) can diced tomatoes; 1 teaspoon Old Bay seasoning; 1 tablespoon sugar; 1 cup dry sherry (or brandy, cognac, dry white wine); 2 teaspoons kosher salt; 1 teaspoon ground black pepper; ¼ cup all-purpose flour; 1 cup half-and-half or heavy cream; 1 lb peeled/deveined shrimp; 1 cup fresh jumbo lump crab; 2 tablespoons fresh parsley, chopped; Toasted bread or croutons, for serving; Juice of ½ a lemon; 2 tablespoons of mayonnaise; 1 teaspoon Dijon mustard; 1 teaspoon whole grain mustard; 1 tablespoon fresh parsley, chopped; Salt and pepper, to taste