Set your sous vide device to 195 degrees. Then, peel potatoes, roughly chop them, and place them in a bowl of cold water until all are prepared. Once ready, add potatoes (without water) to a large zip lock bag along with milk, garlic, butter, and rosemary.
Take out the air and seal the zip lock bag using either the water immersion technique or a vacuum sealer. Submerge bag in water and let sit for 1.5 hrs.
Once finished, remove bag and pour liquid into a bowl and reserve. Pass the potatoes through a fine mesh strainer or ricer into a separate bowl to obtain a very creamy consistency. Fold in the gorgonzola, then the milk/butter from the other bowl, and add salt/pepper, to taste. Can top with chives or extra rosemary.