Cut the meat in cubes, season with salt and pepper and leave for half an hour. Then heat half the oil in a pan and stir-fry the meat for a few minutes, until tender. Take the meat out and place aside.
Cut the onion layers into squares. Sauté the onions for 2–3 minutes using the remaining oil. Once golden-brown, remove from heat.
Season the sautéed onion and beef with salt, pepper, paprika and gently stir to mix. Place meat pieces on skewers, alternating between onion and beef.
Warm the vegetable stock and whisk in the flour. Bring this mixture to a boil along with chopped garlic and wine. Simmer for a few minutes to thicken the sauce (wheat flour requires 5 minutes of boiling).
Drizzle the sauce on beef skewers before serving.