Lay one steak, cut side up, on a non-reactive 12 × 18-inch pan. Sprinkle it with half the vinegar, half the garlic, and half the thyme. Place the second steak on top and repeat the process. Cover the pan and refrigerate overnight.Wash and trim the spinach or chard. Discard the stems and blanch the leaves.In a small frying pan, heat the oil and cook the sliced onions slowly until translucent (about 10 minutes).Lay the steak end to end, seasoned side up, overlapping them about 2 inches. Pound the joined ends together to seal securely. Spread the spinach leaves evenly over the meat and place the carrots on top, laying them in a parallel row along the length of the meat, across the grain. Arrange the eggs on top and scatter the onion rings. Sprinkle the entire surface with the parsley, chili and salt.Carefully roll the steaks along the grain into a long, thick cylinder. Using a 10-foot-long piece of cotton twine, tie one end around the roll about 1 inch from the end and knot securely. Holding the twine in a loop near the knot, wrap the remaining length around the steaks about 2 inches from the edge of the roll and feed it through the loop.
