Beef skewers with chimichurri sauce

Ingredients:

• 0.5 cup apple cider vinegar
• 2 tablespoons of sugar
• 1 red onion, thinly sliced
• 1 bunch cilantro, coarsely chopped
• 1 flank steak, 450g, trimmed
• 1 clove of garlic
• 2 tablespoons red wine vinegar
• Juice of half a lemon
• 0.5 tsp red pepper flakes
• 0.5 cups extra-virgin olive oil + extra for greasing

Preparation:

1. Pickled red onions:
   
   Combine vinegar, sugar, and 1 teaspoon of salt in a medium bowl and stir until completely dissolved. Add red onion and 2 tablespoons of cilantro and stir. Cover and let sit at room temperature for 1 hour.
2. Meanwhile, soak 20 wooden skewers in warm water for at least 20 minutes. Slice the steak across the grain into 20 0.3 cm thick strips. Thread one strip onto each skewer, gathering it like an accordion, and set aside until ready to grill.
3. Combine the remaining cilantro, garlic, red wine vinegar, lemon juice, red pepper flakes, 1/2 teaspoon salt, and olive oil in a blender and blend until smooth; transfer to a small bowl.
4. Heat a grill or grill pan over medium-high heat. Season the steak with salt and black pepper. Brush the grill with olive oil and cook the kebabs until charred, about 1 minute per side. Serve with chimichurri sauce and pickled onions.