Spelt Spaghetti with Kombu and Onion Broth

Name: Spelt Spaghetti with Kombu and Onion Broth
Ingredients: 3 tbsp. extra-virgin olive oil; 5 onions, thinly sliced; 3 shallots, thinly sliced; 2 cloves garlic, crushed; 2 leeks, white and light green parts only, thinly sliced on the diagonal; Kosher salt and freshly ground black pepper, to taste; 2 tbsp. sherry vinegar; 1⁄4 cup madeira; 6 cups vegetable stock; 1⁄2 tsp. black peppercorns; 3 small sprigs fresh thym; 1 bay leaf; 1 tbsp. white soy sauce; 1 (1½″) piece ginger, peeled and thinly sliced; 1 (5″) piece kombu; 8 oz. spaghetti, preferably made with spelt; 1 oz. shelled sea urchin (optional)