Picked up a flank steak today.
I was going to tenderize it under a pile of kosher salt then marinade. But I’m not sure if that’s the right sequence (assuming sequence even matters).
What do you guys think?
With a steak I’d do either/or. For “better” cuts (Not that I don’t love flank steak) I’d go just the simple kosher salt (and fresh ground pepper) route. For a marinade for a tougher cut like flank I don’t think you want or need to do both, because the marinade should do the job of tenderizing- a marinade typically has a trinity of salt & flavoring, acid and an oil that will do the job for you.
marinades don’t tenderize meat.
that is, unless they use an ingredient containing enzymes e.g. fresh pineapple juice.
Why do you even need to tenderize it? I buy flank steak all the time. Just slice it across the grain, it’s plenty tender.
If you really feel the need to tenderize, get a Jaccarder. It’ll tenderize a little bit, and also let whatever rub/marinade you have get a little farther down into the meat.
Option 1: Salt it and let it sit 12-24 hours, then use a salt-free dry rub. This is what I’ll do 99% of the time with a flank or “london broil” (usually top round). Use whatever would have been your marinade as a sauce at the end. Chop some fresh herbs on the same board you sliced the steak, and sweep them with all the board juices into the marinade/sauce.
Option 2: Brinerade. Make a marinade with significantly more salt than most recipes call for, and cut the acid in half. Let sit for up to 8 hours. Dry very well before cooking, or you will have issues getting a good crust before overcooking the meat.
Marinades do not penetrate beyond the very outer layer of the meat, and they do not tenderize the meat. Salt penetrates. Acid breaks down the outer layer of the meat, making it mushy (and pineapple or papaya have enzymes which really break down the meat and make it very mushy, unedibly so if it sits too long).
Ah, but if you score both sides of the flank steak deeply in a criss cross pattern it will penetrate deeper. And marinades don’t so much tenderize the meat as they slowly cook it, similar to citrus fruits and ceviche.
I have more or less perfected an Asian style marinade for flank steak and I must say it’s my life’s work. 
1 large bottle Kikkoman Teryiaki
1/4 cup soy sauce
1/3 cup sherry wine
1/2 cup pineapple juice
1/3 cup brown sugar
2 tablespoons Sambal Oelek (a fiery Asian chili paste with awesome flavor…I suppose you could sub with Sriracha, or Gochu Jang)
3 cloves of garlic, minced
1/2 teaspoon ginger paste or similar equivalent minced fresh ginger
As stated above, I score the flank steak deeply with a chef’s knife on both sides. The marinade I make first, mixing well. A perfect marinating container for flank steak is a fish box. If you don’t know, it’s a long, flat plastic box with a tight fitting lid to prevent spills in the fridge, and it’s also deep enough to contain the liquid. If you know anyone that cooks at a restaurant where there’s fresh fish, they could probably give you one.
I also remove as much of the silverskin/fat/tendon-y bits from the meat as I can while I’m scoring it. Once I place the steak in the liquid, I will typically take some of the ginger paste (I like that over fresh for this because it’s spreadable), the garlic and the Sambal Oelek and use my fingers to spread it over the top side of the steak, pressing it into the scoring.
Ah, I almost forgot two things: secret ingredient is CHINESE FIVE SPICE. I sprinkle some of that on the steak, along with fresh ground pepper before I close the lid and put it into the fridge. Be careful with five spice though…too much is overwhelming.
I marinate for 24 hours, flipping the steak and spooning the liquid onto the top of it several times before cooking.
I never use salt for this, it’s already salty enough. I cook to med rare, let rest for about five minutes then cut it into strips at an angle against the grain, which is so very important for flank (or flatiron) steak.
I promise you this is super yummy.