Bring a large pot of water to a rolling boil.

Season the water generously with salt, then add the spaghetti. Cook according to the package instructions until al dente.

Before draining, reserve about 1 cup of the pasta water.

Drain the spaghetti well and set it aside. Do not rinse it, since the natural starch remaining on the pasta helps the creamy sauce adhere to the strands.

Prepare the Shrimp

If you're using frozen shrimp, make sure they are completely thawed.

Pat the shrimp thoroughly with paper towels to remove excess moisture. This step may seem small, but it makes a major difference when searing shrimp.

Wet shrimp tend to release water into the skillet instead of developing those flavorful golden edges.

Heat the Skillet

Place a large, deep skillet over medium-high heat.

Add the olive oil and 2 tablespoons of butter.

Once the butter has melted and the skillet is hot, you're ready to cook the shrimp.

The combination of butter and olive oil gives the shrimp a rich flavor while allowing them to cook at a relatively high temperature.

Add the Garlic

Add the minced garlic to the hot butter mixture.

Cook for only a few seconds, stirring constantly, until the garlic becomes fragrant.

Do not let it become dark brown. Burnt garlic can taste bitter and will affect the flavor of the entire dish.

Season the Shrimp

Add the prepared shrimp to the skillet.

Immediately sprinkle them with Cajun seasoning, smoked paprika, salt, and black pepper.

Toss the shrimp gently so the seasonings coat them evenly.

Sear the Shrimp

Cook the shrimp for approximately 2 minutes on the first side, then turn them and cook for another 1–2 minutes.

The exact cooking time depends on their size.

They are ready when they become opaque and pink with lightly browned edges.

Try not to overcook them. Shrimp continue cooking from residual heat, and excessive cooking can make them firm and rubbery.

Finish with Lemon

Once the shrimp are cooked, drizzle the lemon juice over them.

Give the shrimp a gentle toss so the citrus mixes with the buttery Cajun seasoning.

Transfer the shrimp to a clean plate and set aside.

Leave the flavorful butter and juices in the skillet. They will become part of the creamy sauce.

Make the Creamy Garlic Parmesan Sauce

Melt the Remaining Butter

Reduce the heat to medium.

Add the remaining 2 tablespoons of butter to the same skillet.

Let it melt, using a wooden spoon or spatula to loosen any flavorful bits left behind by the shrimp.

Add the Cream and Milk

Pour in the heavy cream and whole milk.

Stir gently and allow the mixture to warm.

Keep the heat moderate. The dairy should gently simmer rather than boil aggressively.

Add the Cheese

Gradually add the freshly grated Parmesan and shredded mozzarella.

Stir continuously but gently as the cheese melts into the cream.

Within a few minutes, the sauce should become smooth, creamy, and glossy.

If the sauce becomes too thick, add a small splash of reserved pasta water.

Season the Sauce

Add the Italian seasoning, garlic powder, onion powder, and Cajun seasoning.

Stir until all the seasonings are evenly incorporated.

Taste the sauce before adding extra salt. Parmesan and Cajun seasoning can already contribute plenty of salt.

Bring the Pasta Together

Add the Spaghetti

Transfer the cooked spaghetti directly into the skillet.

Using pasta tongs, toss the spaghetti through the creamy sauce.

Lift and turn the strands several times so the sauce reaches every part of the pasta.

If the sauce is too thick, add reserved pasta water one tablespoon at a time.

The goal is a silky sauce that coats the spaghetti without becoming watery.

Return the Shrimp

Add the cooked Cajun shrimp back to the skillet.

Gently fold them into the spaghetti and sauce.

Allow everything to heat together for about 1 minute.

Since the shrimp are already cooked, avoid simmering them for an extended period.

Finish and Serve

Remove the skillet from the heat.

Give the pasta one final gentle toss.

Serve immediately with fresh parsley and additional Parmesan if desired.

A small lemon wedge on the side is also a great addition for anyone who enjoys a brighter finish.