Preheat the oven to 375 degrees F.
Add the potatoes, cream, milk, garlic and rosemary into a large saucepan and gently boil for 15 minutes until potatoes are just tender and the tip of a paring knife goes through with a little resistance.
Remove from the heat and mash the potatoes with the liquid until smooth and creamy.
Add the sour cream, the stick of butter, salt and pepper and mix together well.
Stir in the eggs, 3 cups of the cheese and cooked bacon.
Butter a 9x13 baking dish. Place the potato mixture in the prepared casserole and top with the remaining cup of shredded cheese. Bake for 35 to 40 minutes, or until bubbly around the edges and heated through.