"Potatoes are easy - we wash and quarter them (skins on, yes), and parboil so that they are partially cooked but well before falling apart. Then add them and their water to the mash. If you cook them too long they will disintegrate and stick your mash. We tried shaving them thin on a mandoline and not cooking them, but actually had better results with larger chunks partially cooked. We use 2 row malt only - good malt should have plenty of enzymes, you're not getting sugar (or not much) from the spuds, just starch. Hence the starchiest potatoes you can get are best. Our very favourite version of the Hell's Kitchen used a Russian Blue potato which is really starchy. We use about 10% potatoes in the mash."