Heat half the olive oil in a cast iron skillet over medium heat until the surface shimmers.
Add two sandwiches and cover with foil.
Weigh it down with a heavy skillet and one or two heavy cans, or a brick covered with aluminum foil.
Cook until the sandwiches are brown on the bottom (3 to 5 minutes), remove the weights, turn the sandwiches over, and cook until brown on the other side.
Repeat with the remaining oil and the other two sandwiches.