Prepare the grill for direct grilling over medium heat. Reduce the balsamic in a wide saucepan over medium heat until very thick, about 15 minutes. A wide pan increases the surface area of the liquid to speed the reduction.
Remove from heat and reserve in the saucepan.Generously brush the bread slices with olive oil. Sprinkle liberally with good quality sea salt. Grill over direct heat until nicely marked and lightly toasted, turning once, about 3 minutes per side.
It is difficult to grill it too little, but easy to grill it too much. Be careful not to let the bread dry out. Remove the bread from the grill.
One four individual plates, place 1 slice of bread, 1 slice of tomato, a couple slices of cheese and 2 basil leaves. Drizzle lightly with balsamic reduction.
If necessary, re-heat the balsamic reduction over low heat until is liquid enough to drizzle from a spoon. Serve with steak knives and forks.
