Preheat the oven to 350°F (176°C).
In a pot of salted boiling water cook the pasta according to the package instructions. Then drain well.
Cook the sausage in the oven to an internal temperature of 155°F (68°C) using a thermometer. Set aside then chop into bite sized pieces before using.
Melt the butter in a saucepan over medium heat. Whisk in the flour and stir for about 1 minute until bubbly and golden brown.
Gradually whisk in the milk until smooth. Add in the cheese and continue to whisk often until the sauce starts to thicken to a smooth velvet consistency. Once the sauce is thick and creamy turn the heat to low.
Warm the bread in the oven for 2 to 3 minutes.
Stir the pasta into the cheese sauce until it is fully coated. Season with salt and pepper to taste. Then stir in the sausage.
Mix together the sparkling water and lemon. Serve over ice if desired.
Serve the mac and cheese with lemon spritzer. Garnish with parsley if using.