Make the brine by mixing the water, salt, Prague powder #1, brown sugar and pickling spice in a nonreactive container. Stir to dissolve well. Place the well-dissolved mixture in a stainless steel pot and bring to a boil. Simmer for 5 minutes and cool to room temperature.
Put the beef in a nonreactive container and cover with brine. Refrigerate. Allow the beef to stand in the brine for 14 days. Turn the meat every 2 days to ensure complete and uniform brining. Remove the beef from the brine. Combine the bay leaves, garlic, mustard seeds, pepper, red pepper, and coriander. Rub this mixture into all surfaces of the beef. Place the beef in a plastic bag with any excess rub. Seal the bag well. Hold the meat in the cooler at 35-38 degrees F for 5 days. Turn the bag once each day.
To cook, remove the beef from the bag. Do not discard the juices. Put the beef and juices in a large pot with water to cover. Bring quickly to a boil. Reduce the heat and simmer for 4 hours or until the meat is fork tender. Add water if necessary to keep the meat covered. Refrigerate the meat in the cooking liquid until it has cooled completely. Clean and dice the meat into approximately half inch cubes.
For the corned beef hash, sweat the shallots and garlic in the butter until tender add the glace de viande. Fold in the rest of the ingredients and adjust the seasoning with salt and pepper. Divide into 4 and wrap each with a cabbage leaf and then caul fat. Refrigerate.
For the potato puree, cover the potato with cold water, add a little salt bring to a simmer and cook until tender. In a separate pan bring the cream and butter to a boil. Strain the potato and transfer to a blender add the heated butter and cream a little at a time to reach desired consistency. Adjust seasoning with salt and add chopped parsley.
To make the sauce, sweat the shallots in 2 tablespoons of the butter until tender. Add the white wine and reduce until almost sec. Add the demi glace, bring to a simmer and reduce to sauce consistency skimming often. Add the remaining butter, thyme and cracked black pepper and salt to taste.
To complete the dish, sauté the caul fat wrapped corned beef parcels on both sides over a medium heat until the fat has melted, is golden brown and hot all the way through. In a deep well bowl place a large spoonful of the potato purée. Place the corned beef on top and spoon about a tablespoon of the sauce over the corned beef. Garnish with micro parsley.