Preheat the oven to 375 degrees.
Spray a 9"x13" baking dish with non-stick spray.
Cook the pasta to al dente per the package directions and drain well.
Add one tablespoon butter, one tablespoon olive oil, the shallot, minced garlic, and red pepper flakes to a large skillet or fry pan. Then turn on the stove heat to medium. Cook until garlic starts to turn golden, about 2 minutes.
Turn the heat to high and add half of the shrimp in a single layer to the bottom of the pan, seasoning with salt and pepper. Cook for 1-2 minutes and then flip. Cook for 30 seconds to 1 minutes just until the shrimp is slightly opaque. The shrimp should be slightly under-cooked as they will continue to cook up in the oven.
Immediately remove the shrimp from the pan including any bits of garlic. Repeat the process with the second half of the shrimp, adding additional oil and butter if no drippings remain.
Turn the heat on the pan down to medium and melt the 3 tablespoons of butter for the sauce.
Add the flour and cook, stirring constantly, for two minutes.
Slowly begin whisking in the milk until everything is smooth and well incorporated.
Cook for an additional 1-2 minutes until the sauce begins to thicken. It does not need to boil. Remove the pan from the heat.
Add the salt, pepper, nutmeg and then the cheeses in batches, whisking to combine until the cheese is completely melted and smooth.
Stir in the shrimp and drippings and the cooked and drained macaroni into the sauce. Pour into the 9x13 greased baking dish.
Combine the Breadcrumb Topping ingredients together in a small bowl and then sprinkle evenly over the tops of the mac and cheese.
Bake for approximately 25-30 minutes until the sauce is bubbly around the edges and the breadcrumbs have begun to brown.