Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package directions until al dente, about 8 minutes. Drain and set aside.

In a large pot or Dutch oven over medium heat, melt the butter. Add the flour and whisk constantly for 2-3 minutes until the mixture turns golden and smells nutty, creating a light roux.

Gradually whisk in the milk and heavy cream, stirring constantly to prevent lumps. Continue cooking and stirring for 4-5 minutes until the sauce thickens and coats the back of a spoon.

Stir in the Cajun seasoning, garlic powder, cayenne pepper, salt, and black pepper. Mix well to combine all the spices into the sauce.

Reduce heat to low and add the shredded cheddar and pepper jack cheese in batches, stirring after each addition until completely melted and smooth.

Add the cooked macaroni to the cheese sauce and stir gently until all the pasta is evenly coated with the creamy Cajun cheese sauce.

Taste and adjust seasonings if needed. Serve immediately while hot and creamy, garnished with extra Cajun seasoning or fresh parsley if desired.