Step 1

Preheat the oven to 350 degrees F (175 degrees C).

Step 2

Pour 5 cups water into a saucepan. Cover and bring to a boil over high heat. Add macaroni and boil until tender yet firm to the bite, about 8 minutes.

Step 3

Meanwhile, melt butter in a saucepan over medium heat. Stir in flour until a smooth paste is formed. Slowly pour in milk, stirring to incorporate. Add 1/2 cup Cheddar cheese, sour cream, and Cajun seasoning. Drain macaroni and stir into the sauce. Add frozen shrimp and stir to combine.

Step 4

Pour macaroni mixture into an oval au gratin dish. Top with panko bread crumbs and 2 tablespoons Cheddar cheese.

Step 5

Bake in the preheated oven until bubbly and golden, about 20 minutes.