Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking or casserole dish.

Cook the penne pasta in a large pot of salted boiling water according to package directions until al dente. Drain well and set aside.

In a large saucepan, melt 1/2 cup of butter over medium heat. Add the 2 cloves of minced garlic and cook until fragrant, about 30-60 seconds, being careful not to brown it.

Slowly whisk in the heavy cream. Bring the mixture to a gentle simmer and cook for 3-5 minutes, stirring occasionally, until it starts to thicken slightly. Remove from the heat.

Gradually whisk in the 1 1/2 cups of freshly grated Parmesan cheese until the sauce is smooth and creamy. Stir in the salt, black pepper, and nutmeg. Set aside.

In a large skillet, melt 2 tbsp of butter over medium-high heat. Add the 4 cloves of minced garlic and sauté for 30 seconds until fragrant.

Add the shrimp and scallops to the skillet in a single layer. Cook for 1-2 minutes per side, just until the shrimp turn pink and the scallops are lightly seared. Do not overcook them as they will finish cooking in the oven. Remove the seafood from the skillet and set aside.

In a large mixing bowl, combine the cooked pasta, the Alfredo sauce, the cooked shrimp and scallops, the lump crab meat, and the frozen peas. Gently toss until everything is evenly coated.

Pour the mixture into the prepared casserole dish and spread it into an even layer.

In a small bowl, prepare the topping by combining the panko breadcrumbs, 3 tbsp of melted butter, 1/4 cup of Parmesan cheese, and 2 tbsp of chopped fresh parsley. Mix until the breadcrumbs are evenly moistened.

Sprinkle the panko topping evenly over the casserole.

Bake, uncovered, for 20-25 minutes, or until the sauce is bubbly and the topping is golden brown and crisp.

Remove from the oven and let the casserole rest for 5-10 minutes before serving. This allows the sauce to set slightly. Garnish with additional fresh parsley if desired.