Peel potato skins and cut into 1 inch chunks. This helps potatoes boil faster.
Add potatoes to a large stockpot and cover with water, at least 1" above the potatoes.
Heat on medium high and boil potatoes until tender, easily sticking a fork into them. This typically takes about 15 minutes.
Carefully drain excess water and return soft, warm potatoes to pan.
Directly on the potatoes, add milk, sour cream, 4 tablespoons butter, Dijon mustard and minced garlic.
Mix all ingredients together well and season with salt and pepper.
Preheat oven to 375.
Grease a 1-1/2 quart casserole dish with nonstick cooking spray.
Spoon potato mixture into casserole dish and spread evenly.
To the top of the casserole, add shredded cheese evenly over the potatoes.
In a small bowl, combine bread crumbs and 2 tablespoons melted butter. Mix well.
Sprinkle bread crumbs on top of cheese in dish.
Bake potato casserole for 20-25 minutes or until the center is hot. Keep in mind that all ovens heat at a different temperature so its important to watch your breadcrumbs.
Remove casserole from oven and serve while cheese is melty.
