Cook the macaroni as per package directions. Make sure to add 1/4 tsp salt to the water to boil the noodles. Drain and set aside.
Mix flour, 1/2 tsp salt, and garlic powder in a small bowl. Set aside.
In a medium saucepan, melt butter over medium heat. Add flour to the butter and whisk to combine.Cook for about 1 minute until mixture is slightly brown. It will be thick. Add 1 cup of milk and whisk until the mixture is smooth.Add sour cream or cream cheese and whisk until smooth. Cook on medium heat until mixture is thick and sticks to the back of the spoon. Reduce heat to low and add cheddar cheese. Whisk until cheese is melted and mixture is smooth.
Season to taste.