Peel the russet potatoes.
Slice them into planks, then strips and dice into bite sized cubes.
Place the cubed potatoes into a pot of water, bring to a boil and cook for 8 minutes.
Remove and drain the potatoes in a colander then side aside to let them cool.
Preheat the oven to 350 degrees. Coat a 9 x 13 baking dish with butter or cooking spray.
Melt the butter over medium heat then add the diced onions.
Cook for a few minutes, stirring occasionally, until softened.
Add the minced garlic and cook, stirring constantly, for 1 minute.
Sprinkle in the flour and stir, cooking for 2-3 minutes.
Very slowly, pour in the half cup of broth and half cup of whole milk, while whisking.
Continue to stir until thickened, about 6-8 minutes.
Season with sea salt and freshly cracked pepper, to taste. Remove from the heat.
Add the cooked and drained potatoes to the saucepan with the thickened gravy along with the sour cream, colby cheese, and green onions.
Stir until well combined; taste and season with sea salt and freshly cracked pepper, to taste.
Pour into the prepared baking dish.
Place into the oven and bake in the oven for 1 hour or until bubbly and lightly golden.
Remove from the oven and let cool for about 15-20 minutes before serving. Enjoy.