Makes: 4 Tacos Scientificos
Total kitchen time: 30 minutes (+12 hours cooking time)
Special equipment: Vacuum sealer, sous vide water oven

Shopping list:

• 1 lb. flank steak
• 1 tsp. Mexican seasoning blend
• 2 tbsp. lime juice
• 1 large red onion, diced
• 1 tsp. olive oil
• 1/4 cup dark brown sugar
• 1 tbsp. sherry vinegar
• 1 pinch salt
• 4 four tortillas
• 1 cup crumbled goat’s cheese
• 1/2 cup sour cream
• 1 bunch cilantro

1. Pat the steak dry and coat all sides with Mexican seasoning blend and lime juice.  Vacuum seal the steak in a bag large enough that the meat lays flat (but still fits in your water oven).  Cut the meat into two pieces and seal separately, if needed.  (If you’re not cooking your steak sous vide, place it in a zip-top bag or a covered shallow dish and let it marinate overnight). Note: although it might be tempting to add aromatics like garlic to the marinade, don’t! Your kitchen will smell like ass by the time the meat is done.
2. Set your sous vide water oven to 56°C.  Add the vacuum sealed steak, making sure the meat stays submerged.  Cook for a minimum of 1 hour, up to 48 hours.  The picture above shows the meat after cooking for 12 hours, which was perfectly tender.
3. Meanwhile, heat 1 tsp. olive oil in a medium saucepan over moderate heat.  Add the red onion and reduce the heat to low.  Let the onion sweat 5 minutes, until it is slightly translucent, but not browned.  Add the dark brown sugar, sherry vinegar and salt and stir to combine. Simmer 30 minutes, stirring occasionally, and making sure the mixture doesn’t boil or burn. 
4. Remove the bag from the water bath and let the meat rest, still in the bag, for 10 minutes before searing.  Remove the meat from the bag and pat dry on all sides.  Sear with a blow torch, under the broiler, or in a smoking-hot pan.
5. Slice the meat perpendicular to the direction of the muscle fibers, and on a sharp bias. 
6. Assemble the tacos: tortilla, sour cream, steak, cheese, onion compote, cilantro.  Enjoy!

Cooking the steak sous vide rather than just grilling it may sound like a pain in the ass since you have to plan 12 hours ahead.  However, the hardest part of cooking flank steak is getting your timing right. Leave it on the grill 1 minute too long and it’s overcooked and tough; take it off too early and it’s raw.  And, if you’re entertaining company, you may be more focused on your margarita than your steak.  Cooking your meat sous vide lets you be laissez-faire with your timing – sometimes I even sear my steak before company arrives and return it to the water bath to keep it warm until we’re ready to eat.