Brush pan/parchment with evoo, drizzle with maple syrup & balsamic glaze, set sliced onion on top, sprinkle with salt, pepper, and thyme, lay puff pastry on top (I used store bought frozen), brush with egg wash. Cook at 350° until puffed.
This is it. This is all you have to do. I subbed in portobellos on half because I thought it would be good. It was. Next time though I will slicke the bellos thin.