Cut off all the skin. Pretend like the tongue is shaped like a brick, and with a very very sharp knife you will cut off each 'side', once all 4 surfaces or sheered away, you can cut off any remaining bits of skin and then clean it up of bloody parts if you need to to make it look less raunchy and more visually appealing. Then I would start at the thick end and cut off very thin slices, play around with the width to find what you like best. Good condiments for this food include real raw mayo, good quality mustards, hopefully raw, sauerkraut, or any raw sauce you can think of out there. This meat at the back of the tongue is very tender and a pleasure to eat. The meat at the front is delicious too, but requires chewing or very thin shaving, the meat has a good flavor and should not be wasted, soaking it in something for a while will probably help too, maybe some milk or cream or the juices of the kraut (though this will have some sort of impact on the nutrition.
Play around, experiment, its delicious and I just finished up my last one yesterday morning with my puppies, mmmM!
One last thing, this way of living requires of most to have very sharp knives, especially a good chef's knife. I run my Forchner over a whet stone every couple days, doing this guarantees me a hair splitting edge, scary sharp, and cutting any meats is a pleasure because this knife treats them as if they are warm butter. I recommend this style of knife because its so versatile, and you cant beat the brand for quality and value. Learning to use a whet stone is easy [and critical for people like us], keep the blade at about a 20 degree angle and drag it along once on each side, then repeat about 50 more times. Best to start with a new knife with a good edge, you may become frustrated trying to resurrect grandmas old cutlery.
