How to Come Out on Top with Underblade
Underblade steaks and roasts have the most tenderness of any beef cut in the chuck section, which includes the shoulder along with a little of the neck, upper "arms" and ribs. But saying the underblade has the most tenderness of the chuck region is a bit like saying top round has the most tenderness of the beef rump – the whole subprimal is tough, so you're really just describing the least tough, rather than the most tender, cut from the section. That said, you can wrangle beef chuck underblade, which has arguably the "beefiest" flavor of all the beef cuts, into tenderness with a little gentleness.
Why So Tough?
Like all cuts from the chuck subprimal, underblade has a lot of connective tissue, and a thick seam of cartilage running through its center, as well. This works to your advantage, though, and makes cuts from the chuck, the underblade in particular, more flavorful than other beef cuts.
As the underblade cooks, the cartilage and other connective tissues render down to a flavorful gelatin, essentially self-basting the interior muscle fibers you just can't reach from the surface. In this case, what appears to be a "bug" turns into a feature with the proper cooking method.
What to Do About It
Whether you have an underblade steak or a roast, you have to braise that bad boy to tenderize it – roasting, pan-frying or grilling turns underblade into nothing short of edible shoe leather. Marinades have little to no effect on its toughness, either, so "low and slow" is pretty much your only option.
Sear the underblade in a saute pan. Season the underblade (roast or steaks) to taste with salt and pepper, and sear it in a few tablespoons of olive oil on the stove over medium-high heat. Transfer the underblade to a deep, oven-safe pan, and heat the oven to 325F.
Add the secondary ingredients. You always want to include a a bay leaf and a couple roughly chopped onions, carrots and celery ribs to any braise for their aromatic properties. Although optional, a can of crushed tomatoes helps break down the connective tissue faster. If you use tomatoes, add 1 cup of beef stock; if you don't use tomatoes, add enough beef stock to reach about halfway up the sides of underblade.
Braise the underblade until tender, about 3 to 3 1/2 hours. Cover the roasting pan with a tight-fitting lid or aluminum foil. Check the tenderness after about 3 hours; the meat should fall apart easily with a fork.
Make a delicious pan gravy. Don't let those pan juices go waste. Strain the juices through a sieve and into a saucepan. Bring the juices to a simmer, and combine 1 tablespoon each flour and butter into a ball. Drop pieces of the flour and butter into the saucepan while whisking vigorously. Simmer the gravy for about 10 minutes, and season it to taste with kosher salt and freshly ground black pepper.
You can braise underblade on the stove if you have a Dutch oven or other large pan with a tight-fitting lid. Sear the underblade in the pan; add the secondary ingredients and braise, covered, for 3 to 3 1/2 hours.
Just because marinating doesn't have much tenderizing effect doesn't mean you can't take advantage of the flavor it contributes. If you choose to marinate, 4 hours to overnight is the best range for maximum flavor introduction; much longer and the surface of the meat start breaking down to mush.