1. Preheat the oven to 400 degrees and line a baking sheet with parchment paper.
  2. Unfold the puff pastry sheet on the piece of parchment or on a lightly floured counter. Use a 2” round cutter to trim out 12 circles of dough. You may have extra dough- feel free to freeze and save or make a double batch of puffs.
  3. Use a smaller round cutter or a paring knife to score a ¼” border around the edge of each pastry circle and prick the inner circle with a fork a few times. Place in the fridge to keep cool while you prep your filling.
  4. In a sauté pan over medium heat, melt the Kerrygold butter and olive oil together. Add the thinly sliced onions and cook, stirring regularly, until the onions are soft and translucent.
  5. Add the thyme, salt, and pepper, and continue to cook until the edges of the onions start to get dark.
  6. Add the mustard and Worcestershire and stir to combine. Remove from the heat.
  7. If desired, add a teaspoon of water to the lightly beaten egg and use a pastry brush to paint a thin layer of the wash on top of each tart.
  8. Divide the sautéed onions among the rounds of , piling a few onions only into the inner circle of each round.
  9. Depending on the size of your onion you may have a little leftover.
  10. Divide the Kerrygold Blarney Castle cheese among the tarts, sprinkling it and the parmesan directly on top of the onions.
  11. Bake in the preheated oven for about 15 minutes or until the puffs have risen and the edges are golden.
  12. Remove from oven and set aside to cool slightly.
  13. Add a teaspoon of the bacon jam to the top of each tart and serve!