If you're a foodie, you love a well stocked supermarket, and I could spend the whole day just browsing around the large and boldly colorful, sparkling clean Mexican Mercado (supermarket) in my California town. For those who are accustomed to the typical American grocery, the Tortilleria (the tortilla factory), the Taqueria (the food court) and Panaderia (the bakery) are a terrific bonus, but the Carnicería (the meat dept) where meat does not come in plastic trays, is my first stop. 
With so much to see, it can be somewhat confusing to a gringa like me. The courteous and helpful Mexican Carnicero (butcher) offers a huge selection of every sort of fresh USDA meat imaginable, all displayed in a gleaming meat case that must be a hundred feet in length. The customers cue up to select from a dizzying variety of cuts that will be wrapped up in butcher's paper for you. Even the cuts of meat may look unfamiliar because it is usually cut along the muscle groups, so there is less bone included... more bang for the buck! American butchers cut cross several muscle groups and take a crosscut section of bones along with the meat, which of course adds to the overall cost we pay.
The first thing you'll notice is that Mexican Carne De Res (beef) is generally cut very thin, and its only about 1/4 inch thick. While you may not see large roasts or thick, juicy American style steaks, you can certainly ask the Jefe de Carniceros (Chief Butcher) for any special cut you'd like or preorder in advance. Mexican cuts are thinner for two reasons; first, like most other countries, meat is not consumed as a high percentage of the diet in Latin America. Secondly, the wonderfully complex flavors of Mexican cuisine make the most of thin cuts of meat to stretch the food budget with traditional recipes that add delicious combinations of robust ingredients and piquant seasonings.
Another thing that you will notice in the Carnicería is that the beef also looks leaner and less marbled than its fatty, corn fed American cousin, and the meat is not generally aged so its very bright red in color. The fat may have a yellow tint due to the vitamin A in grass from cattle that are raised on pasture rather than feedlots. Not only does the Carnicero do a painstaking job of removing most of the fat, but a leaner beef carcass is preferred... a plus if you're trying to eat healthier meals.
This makes Mexican beef an excellent choice for the pressure cooker where it benefits from moist heat cooking methods like braising, steam-roasting, poaching, or stewing. For this recipe, the cut of beef I bought at my local Mexican Mercado, was a Clod Steak. This is just one of the many different names for a Boneless Shoulder Steak, which can also be labeled as an English Steak, a London Broil, or Swiss Steak. It's a fairly cheap cut of beef from the chuck, that's the shoulder section of the steer between the ribs and the front chest (brisket). Because the big muscle groups in the chuck are heavily exercised and contain a lot of connective tissue, they are naturally very flavorful, but less marbled and tend toward toughness… perfect for the pressure cooker.
The pressure cooker, with its thick base does a very good job in caramelization, an important cooking trick that not only adds color, but also flavor, to many foods. Caramelizing onions is just cooking them for 10 to 20 minutes to get a nice caramel brown color which develops a rich, sweet flavor as the natural sugars within the onion begin turning to caramel. It's important to have all the onion pieces roughly the same size and shape so they cook evenly otherwise the smaller pieces will start to burn before the larger pieces can caramelize.The onions will lose as much as two-thirds of their volume as the water within them evaporates. Stir them often as they begin to brown, and watch closely as they'll quickly go from light tan, to golden. The deeper the color; the richer the flavor, and with care, you can get a deep mahogany brown, but the danger of burning is high, so I'm happy with the golden brown.
Lightly brown the strips of beef in hot oil and then toss in the green stuff. If you are shopping at the local mercado, buy a mild Mexican chile pepper to add a zesty piquant flavor without too much heat, and you'll also need some peppery cilantro leaves add to the unique Mexican taste. Add other hot peppers if they appeal to your taste buds, or just stick with an assortment of colorful bell peppers if you're more timid.The peppers will loose a lot of water during cooking, but that ads to the flavor of the au jus dipping sauce. When you remove the lid, divide the
meat mixture between the sandwich rolls and top with a slice of Jack cheese while its still hot.Taste the dipping sauce and adjust the flavors to your taste. I added more salt and a big splash of Mexican style jalapeno hot sauce before spooning it into small ramekins on each serving plate.
