Pour the 6 cups of fish or vegetable stock into a saucepan and bring it to a gentle simmer. Keep it warm over low heat throughout the cooking process.

Heat the olive oil and butter in a large, deep skillet or wide saucepan over medium heat.

Add the diced onion and cook until softened and translucent, approximately 4–5 minutes.

Add the minced garlic and cook for another 30–60 seconds, stirring frequently so it becomes fragrant without browning.

Pour in 1 cup additional fish or vegetable stock and 2 tablespoons lemon juice. Stir and bring to a gentle simmer.

Add the Arborio rice. Cook while stirring until most of the liquid has been absorbed.

Add approximately 1 cup of the hot stock to the rice. Cook over medium to medium-low heat, stirring regularly until most of the liquid has been absorbed.

Continue adding the warm stock about 1 cup at a time. Allow each addition to be mostly absorbed before adding the next.

When approximately 2 cups of stock remain, whisk the tomato paste into the remaining hot stock until smooth.

Continue adding the tomato-infused stock gradually, stirring frequently and allowing the rice to absorb the liquid between additions.

When you reach the final cup of stock, add it to the rice along with the shrimp and sea scallops.

Continue cooking and gently stirring the Risotto Marinara (Seafood Risotto) until the rice is creamy and al dente and the seafood is cooked through. Shrimp should be opaque and firm, while scallops should also turn opaque and reach a safe doneness.

Remove the risotto from the heat. Stir in the remaining tablespoon of fresh lemon juice.

Season with salt, freshly ground black pepper, and optional crushed red pepper flakes.

Let the risotto rest for 1–2 minutes. It should remain creamy and loose rather than becoming dry or stiff.

Garnish with chopped fresh parsley and serve immediately.