Peel the onion and garlic. Chop both finely and cook briefly in 1 tablespoon oil until translucent. Stir in ketchup, a little water and vinegar. Stir in the sugar, Worcestershire sauce and chili powder, season with salt and pepper and bring to a boil. Simmer over low heat half-covered, stirring occasionally, about 15 minutes. Remove from the heat and season with sea salt.
Rinse steaks and pat dry. Crush the peppercorns in a mortar and rub over the steaks. Season with salt and fry in a pan in the remaining oil until browned, about 2 minutes on each side. Reduce the heat and continue cooking to the desired degree of doneness (medium: about 2 minutes per side).
Remove the steaks from the pan, let rest a few minutes and cut into strips. Serve with the sauce.
