In a pot of salted boiling water cook the pasta according to the package instructions. Then drain well.
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.
Heat a nonstick pan on medium heat. Once hot, saute the sausage to golden brown.
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 lemonade. Serve over ice if desired.
Serve the mac and cheese with sparkling lemonade. Garnish with chives if using.