Make the pasta: In a medium to large sized pot, boil 3 quarts of water with 2 teaspoons of salt. Once boiling, add fettuccine and boil for 11 minutes or until pasta is al dente.
Make the sauce:
While the pasta is cooking, make the sauce: In a medium saucepan, melt ½ cup butter over medium heat. Be careful not to burn the butter. Once butter is melted, pour in1 cup of heavy cream and stir well for 2-3 minutes. Once the mixture starts to simmer, add in 1 tablespoon of garlic, ¼ teaspoon salt, and ¼ teaspoon freshly ground pepper. Use a whisk to combine all ingredients evenly. Add in ¾ cup of parmesan cheese and continue to whisk together. The cheese will start to get melty. It’s important that you continue to whisk the ingredients together so that the cheese does not separate from the cream. Turn heat to low, continue to slowly whisk until shrimp is cooked. The sauce will thicken as it reduces in temperature.
Make the shrimp:
While the sauce is thickening, make the shrimp: In a large saucepan, over medium-high heat, add 1 tablespoon butter and 1 teaspoon of minced garlic and saute garlic for 1-2 minutes. Using thawed shrimp, pat them dry and sprinkle with salt, pepper, and cajun seasoning on both sides. Once the butter has melted, add shrimp and cook for 1 minute on each side or until the shrimp turn bright pink. Leave the shrimp in the large saucepan as you will be adding the pasta and sauce to this same pan.
Combine all ingredients: (If your saucepan is not large enough to combine all ingredients, you can serve the pasta and add the sauce and shrimp on top separately.) Add pasta and sauce to the large saucepan with the shrimp. Using tongs, mix together and serve.