Preheat a cast iron or other heavy-bottomed pan to medium heat. Add 3 tbsp butter or oil, and allow to heat up. Add the onions and reduce heat to medium low. Cook slowly, stirring often to prevent scorching, until onions are translucent and caramelized. Add water during this process if onions begin to stick. May take up to 20 minutes.
Stir in vinegar and honey to the same pan, and cook for an additional 5-10 minutes until a syrupy-thick mixture forms. Remove from heat and keep warm.
Heat a cast iron pan to medium-high heat and preheat the oven to 400 degrees. Season steaks with a generous amount of salt and pepper. Heat the additional 1 tbsp of butter or oil in the pan, and then add steaks. Cook on one side until browned. Flip and cook other side until equally browned. Place pan in oven for 3-6 minutes, or until steaks reach 125 degrees. Remove from oven and let sit for 2-3 minutes.
Place each steak on a plate, and top with onion confit. Serve with mashed potatoes, asparagus, or your choice of sides.