Thaw the puff pastry sheets according to the manufacturer instructions. Unfold the sheets and lay them on baking sheets. If the pastry sheets are touching each other, lay them on 2 different baking sheets. Using a fork, prick the surface several times, leaving a half a inch border all around.
Preheat the oven to 400 F. Now get the prepared sheets in the oven for about 10 minutes or until the sheet base is slightly brown.
The sheets could get puffed up in the oven in spite of pricking them. Let the sheets cool on a cooling rack and allow it to settle down. Then transfer it back to the baking sheet.
In the mean time, add oil to a large sauté pan and get the onions inside it. I used the olive oil from the Sun Dried tomatoes. Also add the required salt and the thyme to it. Sauté the onions on medium heat until they are evenly caramelized.
In a small bowl combine the mustard with the heavy cream. Mix well and once the pastry sheets have cooled down a bit, spread this mixture evenly on the sheets, leaving half an inch border untouched.
Now add half the grated cheese to the pastry sheets.
Next add the sun dried tomatoes, onions and the olives (if using) and spread the remaining cheese on top.
Sun dried tomatoes, Onion and Olives
Bake at 400 F for about 15 mins, until the cheese melts.
Serve hot!