In a small saucepan, warm the fish or vegetable stock. Keep warm.
In a large saucepan over moderately low heat, warm the olive oil. Add 1 tbsp of butter and the onion, and sautée, stirring occasionally, until tender (there should be no color), about 5 minutes. Add the rice and toast lightly for 1 minute without letting the rice or onion take on any color.
Add the wine and cook until almost completely absorbed. Add most of the stock (it should come about 1/2 inch above the rice) and bring to a simmer.
Cook the risotto, stirring occasionally, until the rice has absorbed some of the liquid, about 8 minutes.
Add the clams, mussels, squid, scallops, and tomatoes, and continue cooking, stirring occasionally, until the seafood is cooked and the rice is al dente, about 6 minutes more. As the rice continues to absorb the liquid, add more as needed. Cook it a few minutes longer if you prefer a softer rice.
Remove the risotto from the heat and add parsley, garlic, brandy, olive oil, Parmigiano-Reggiano, and the remaining 2 tbsp butter. Stir well to release the starches and make the risotto creamy.
Season to taste with salt and pepper, and serve immediately.