Dice the onions, put them into a pan, add a good dash of olive oil and sauté until softened on low heat. Add the brown sugar and let it slightly caramelize. Deglaze with the port wine and the balsamic vinegar and slowly boil down until the liquid is dissolved respectively becomes sticky.
Halve the Ciabatta, spread the beef fat/butter on to the bread and toast the it on the hot grill.
To finish the Sandwich, spread some Dijon mustard on one the bottom part of the bread, add the cheese and the rocket salad. Then lay on some thinly sliced roast beef slices, add the balsamic onions and enjoy.
Stay tuned and see you soon!