Prepare the marinade by mixing garlic, onion, ginger syrup, sambal and kecap manis. Slice the steaks into small strips, mix with the marinate and let it stand for 15 minutes.
Heat oil in a skillet and add onion. Bake for 3 minutes. Add the meat and marinate and fry for five minutes. Brown the meat on all sides.
Heat oil and add onion and tomato paste, bake for 3 minutes. Add the sherry, kecap manis, brown sugar, curry sauce, water and vinegar. Mix well. Bring to the boil on high heat while stirring. Then turn the heat to low. Mix the cornstarch with the leftover water in a small bowl until it's dissolved. Add to the sauce and mix well. Let the sauce simmer for a few minutes until it becomes thicker and glazy. Turn off the heat. When the meat comes out of the oven, pour the sauce on top of the flesh.