Preheat the oven to 375.

Pour the guinness (or red wine or hard cider) and broth (or cooking liquid from the corned beef) into a medium saucepan, that will fit your head of cabbage, over high heat. Add more broth so there is at least an inch of liquid in the base of the pan, more is best.

Remove the core from the cabbage head by cutting a circle around the base. Place the entire head into the simmering beer & broth, cover with a lid or even a baking sheet.

As the cabbage steams the leaves will become easier to peel away with tongs. Pull each leaf off individually. Dunk each leaf deeper into the beer to simmer for about 20 seconds more. Remove to a drying rack or splatter guard on top of a plate or tray. Allow each leaf to drip and cool slightly.

When the leaves have each been cooked, allow the guinness to boil away and reduce in half. Add the mustard and maple syrup as it simmers. Smash or chop the cooked potatoes.*

Place a whole cooled leaf of cabbage in your hand, fill a couple tablespoons of the smashed potatoes and torn up pieces of cabbage in the center. Finish with a few shreds of the corned beef. Roll it up and place seem side down. Repeat with the remaining cabbage leaves, filling until your pan is full or you run out of ingredients. When the beer is reduced, swirl in the heavy cream if using and pour it over the cabbage rolls. Place in the oven for about 30 minutes until the cabbage is tender and hot when you touch the center most roll.

*If your potatoes are not cooked, place big chunks in a small pot of additional broth or water lightly salted. Bring up to a simmer for about 15-20 minutes until you can easily smash it with the back of fork. Strain the excess liquid and roughly smash the potatoes. Add salt to taste, if needed.