Creole Shrimp Mac and Cheese

1 (8 ounce) box elbow macaroni
4 tablespoons unsalted butter, divided
12 ounces uncooked medium shrimp, peeled and deveined
2 teaspoons Creole seasoning (such as Tony Chachere's®)
2 cloves garlic, minced
2 tablespoons all-purpose flour
2 cups half-and-half
1 cup shredded sharp Cheddar cheese
1 cup shredded Monterey Jack cheese
1 tablespoon Creole mustard

Bring a large pot of lightly salted water to a boil.
Cook elbow macaroni in the boiling water, stirring occasionally, until tender yet firm to the bite, about 8 minutes.
While macaroni is cooking, melt 1 tablespoon butter in a large skillet over medium heat.
Add shrimp; sprinkle with Creole seasoning.
Cook, stirring continually, for 4 minutes.
Add garlic and cook until shrimp is pink, about 2 minutes.
Turn off heat.
Drain macaroni and rinse under cold water to stop the cooking; set aside.
Return the pasta pot to the stove and melt remaining 3 tablespoons butter over medium heat.
Add flour and whisk until dissolved, about 2 minutes.
Add half-and-half; heat for 3 minutes.
Whisk in cheeses until melted, about 5 minutes.
Add mustard; cook for 2 minutes.
Turn off heat.
Add reserved macaroni and shrimp.
Stir until heated through.