Bife à Cebolada

Take the beef out of the refrigerator 10 minutes before cooking so it isn't cold straight from the fridge. In a small bowl, mix the water with white wine vinegar.

Slice the onion into half-rings about 5 mm thick, pat the beef dry with a paper towel, and season with salt and black pepper.

Heat a large skillet well over medium heat. Add 1 tbsp olive oil, lay the beef in a single layer, and sear for about 2 minutes, without moving it, until a golden crust forms.

Flip the beef with tongs and cook for about 2 more minutes. Transfer the steaks to a plate and cover to keep warm.

Return the skillet to medium heat, pour in the remaining olive oil, and add the onion. Season the onion with salt and sauté for about 2 minutes, stirring occasionally, until golden.

Pour in the water and vinegar mixture, scraping up the browned bits from the bottom with a spatula, and cook for about 3 more minutes, until the onion softens slightly and the liquid turns into a sauce.

Turn off the heat, add the butter, and swirl the pan so the butter melts and blends into the sauce. Serve the beef with the onions and pan sauce.