In a medium sauce pan, bring water to a boil and boil noodles according to box instructions. I usually boil one minute LESS than box states.
Drain noodles and keep in colander.
In the same sauce pan, add the unsalted butter and flour and turn fire to medium-low, whisking every few seconds for 2-3 minutes or until the mixture turns golden.
Add in the milk, whisking constantly and then add in the sour cream.
Add in the salt, pepper, and garlic powder and continue to whisk until the mixture is fully incorporated.
Let cook on medium-low heat until the mixture slightly thickens but does NOT boil - about 5 minutes.
Add in the cheddar cheese and stir gently until cheese has completely melted.
Add in the cooked macaroni noodles and stir to combine.
Cover completely and let sit with the fire turned completely OFF for 5 minutes.
Give it another stir and then enjoy!!