Peel, halve and slice <quantity>1</quantity> large onion

Remove the core and the seeds from <quantity>1</quantity> red chili. Small dice it

Remove the core and the seeds from <quantity>1</quantity> green chili. Small dice it

Cut <quantity>1<unit>Kg</unit></quantity> of beef shank into medium cubes

Grease a very hot grill or skillet with melted butter

Sear the meat on all sides until golden brown

Add salt to taste and a little more butter

Add ground black pepper to taste and remove from the heat. Reserve

Add <quantity>1<unit>tbsp</unit></quantity> of extra virgin olive oil to a medium saucepan over medium heat

Add <quantity>2</quantity> grated garlic cloves and stir

Add the onion and chilis. Stir and cook until the onions are soft and golden brown

Add <quantity>2<unit>tbsp</unit></quantity> of tomato paste and stir to combine

Add the seared meat, reduce the heat, and stir

Cover the meat with boiling water

Add <quantity>3</quantity> bay leaves and <quantity>2</quantity> thyme sprigs

Add ground black pepper to taste and cook until the meat is soft

Remove the meat with a slotted spoon

Strain the sauce into a small saucepan

Reduce the sauce until slightly thicker. Add to the meat and the braised beef is ready

Trim, peel and small dice <quantity>1</quantity> onion

Transfer to a bowl, add <quantity>1<unit>tbsp</unit></quantity> of extra virgin olive oil and salt to taste

Add <quantity>2<unit>tbsp</unit></quantity> of white wine vinegar and the juice of <quantity>½</quantity> lime

Add <quantity>1½<unit>tbsp</unit></quantity> of thinly sliced chives and <quantity>½<unit>tsp</unit></quantity> of hot sauce

Add <quantity>1</quantity> small habanada pepper thinly sliced, <quantity>1</quantity> small red finger chili thinly sliced and ground black pepper to taste. Mix it to combine

Adjust seasoning if necessary and plate it. The vinaigrette is ready

Put some butter on the toaster and toast <quantity>10</quantity> hamburger buns cut in half on both sides

Add <quantity>3<unit>tbsp</unit></quantity> of the Braised Beef

Add <quantity>1<unit>tbsp</unit></quantity> of the Brazilian Vinaigrette and cover with the other half of the bread

Add some of the braised beef sauce on top

Finish with fleur de sel and black pepper to taste. Your braised beef sandwich is ready

Enjoy it while it's hot!