Set the sous vide cooker at 52°C / 125.6°F. While the water heats, we'll first prep the beef flank with a good sear.
Take a cast iron skillet and heat it over high heat. Once it's very hot, place the flank on it and sear all sides to lock in the juices.
Don’t let it cook for a long time. 30-60 seconds on each side should be enough.
Once the water it heated, put the beef inside the vacuum seal bag and seal it. No need to add other ingredients into the bag.
Cook the flank for 30 hours.In the meantime, we can prepare the tomato sauce.
Place a pot over medium heat.
Finely chop the 1/2 onion. When done, add 2 tbsp of olive oil and the chopped onion inside the pot. Fry over low heat for 2minutes.
Add the peeled garlic cloves and basil leaves. Also pour in the tomato purée.
Let it cook for 15 minutes over the lowest heat possible.
After 15 minutes, we have a tomato sauce that's almost ready. It still needs to be spiced and seasoned.
Now add everything else. Add the butter, sage leaves, paprika powder, curry powder, dried rosemary, and the 3 tsp of salt in the tomato sauce.
Let it cook for another 2 minutes. Test the sauce and if it tastes a bit acidic, add 1 tsp of sugar to compensate and remove the acidity.
When done, take it off the stove and keep refrigerated until the flank is done.
Once the meat is perfectly cooked, you just need to slice it down and serve glazed with our spiced tomato sauce.