Boil potatoes in a large pot of salted water for about 15 to 20 minutes or until fork-tender. Drain water.
Place potatoes back in pot. Mash with a potato masher or electric hand-mixer until smooth and creamy. Stir in butter, milk and sour cream. Add Parmesan cheese, garlic powder, salt and pepper. Mix until well combined.
For The Gravy
Melt butter in a medium sauce pan over medium heat. Add flour and whisk together for about one minute or until golden-brown. Whisk in water, milk, crushed bullion cubes and pepper. Stir constantly until mixture comes to a boil. Reduce heat to low and continue to stir until thickened.