Start by melting the butter and olive oil together in a large skillet over medium heat. The butter will bubble slightly and create a rich base for your sauce. Avoid browning the butter too much to prevent a burnt taste.
Add the sliced mushrooms, chopped onion, and minced garlic to the skillet. Stir occasionally until the onions are translucent and the mushrooms are soft. Be careful not to burn the garlic.
Sprinkle in the fresh thyme and crushed red pepper flakes, mixing well. A fragrant blend will develop, adding depth to your dish.
Add the white wine and allow it to simmer until reduced by half, which will cook off the alcohol and leave a subtle flavor.
Gently fold in the shrimp and chopped clams, cooking just until the shrimp turn pink. This is crucial as the shrimp will continue cooking in the oven later.
Sprinkle the flour into the mixture, stirring until well combined. Gradually add the heavy cream and half-and-half, whisking to create a smooth, luscious sauce.
Stir in the lemon juice, paprika, and a pinch of salt and pepper to taste. Adjust seasoning as necessary, keeping in mind that the cheese will add more saltiness.
Cook the spaghetti in salted water according to the package instructions until al dente. Drain and set aside.
Toss the cooked spaghetti with the seafood sauce until fully coated, ensuring every strand picks up the creamy goodness.
Transfer the pasta mixture into a greased casserole dish, spreading evenly to ensure it bakes uniformly.
Sprinkle the shredded Parmesan cheese and panko breadcrumbs over the top, creating a beautiful and crunchy crust.
Bake in a preheated oven until bubbling and golden brown. If the top is not browning sufficiently, broil for a minute to achieve that desired finish.