Pour the 6 cups of vegetable or fish stock into a saucepan. Bring to a gentle simmer, then keep warm over low heat.

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

Add the diced onion and minced garlic. Cook for about 5 minutes, stirring occasionally, until softened and fragrant without allowing the garlic to burn.

Pour in the additional 1 cup of stock and lemon juice. Stir to combine.

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

Ladle about 1 cup of hot stock into the skillet. Cook, stirring frequently, until most of the liquid has been absorbed. Continue adding the stock approximately 1 cup at a time, allowing each addition to absorb before adding more. Stop when about 2 cups of stock remain.

Whisk the tomato paste into the remaining warm stock until evenly combined. Bring the tomato-infused stock back to a gentle simmer.

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

With the final cup of stock, add the shrimp and scallops. Gently stir and continue cooking until the seafood is opaque and cooked through and the rice is tender but still has a slight bite.

Taste the Risotto Marinara and season with salt, black pepper, and crushed red pepper flakes as desired.

Garnish with chopped fresh parsley and serve immediately while creamy and hot.