Let's make the topping first. Use a skillet over medium heat to melt the butter, but don't let the pan get too hot. Slowly stir in the garlic and breadcrumbs. Stir continuously until the breadcrumbs are lightly toasted. Remove the pan from the heat and gently stir in the salt, pepper, and minced fresh partly. Set aside and allow to cool

Heat a stockpot filled with salted water. Once the water is boiled, cook the macaroni until it's al dente - the cooking time will be on the macaroni box. After it's cooked, drain the pasta but make sure to reserve a cup of the pasta water. Set aside the reserved pasta water and allow to cool.

While the macaroni is cooking, use a large saucepan to begin the sauce. Using a medium-low heat, melt the butter. Then sprinkle the flour over the top and whisk for one minute. Then, while still whisking, pour in the Guinness, whole milk, half and half, salt, pepper, and mustard. Bring the sauce to a low simmer and, while whisking continuously, cook for 4-6 minutes or until the sauce begins to thicken.

Slowly whisk in the cream cheese and the 2 1/2 grated Irish cheddar cheese. Keep whisking until all the cheese is melted and smooth. Then carefully stir in the cooked macaroni. Once the macaroni is mixed in, stir in the last 1 cup of cheese. Stir this mixture until the cheese is melted and kind of stringy.

Allow the macaroni to cook over a low heat for 3 minutes, stirring continuously. Transfer the macaroni to a large serving dish and sprinkle the bread crumb topping on top. Serve immediately.