I am including a "recipe" for Matambre, even though I have personaly never eaten it nor am I adventurous enough to do so, because it is a typical Argentinian dish and one that many people absolutely love. This recipe comes from an Argentinian friend. I have never tried this "recipe". You can have three other recipes for this dish in Spanish at Mercado del Plata.
"Matambre is a difficult meat cut to get as not all butchers know how to make the necessary and delicate cuts. Matambre is one of the muscles on the surface of the abdomen, it's underneath the skin of the belly. In the US, given where they cut the meat, it's almost impossible to get. To make it, at home we would clean the meat very well and then season it with whatever you like - salt and pepper, oregano, chili powder, etc. Separately you mix several vegetables: carrots (grated or chopped), spinach, onion and/or chopped garlic. You put this mixture on top of the matambre, plus some hardboiled eggs. You roll it from a corner, and tie it together with some meat cord. Cover it tightly (roll it) with a white cloth (the secret is to get the matambre very tight so it doesn't come undone when you cut it). You cook it (preferably in a pressure cooker) in water, where you can put some vegetables to make it taste better. Let it cool underneath some weights, the most common thing is to put it in a big tray, and put on top of it a cutting board and a big book on top ot that."