*If making puff pastry from scratch, please refer to the instructions in the blog post. If using store bought puff pastry, proceed with steps 2-6.
Begin by caramelizing the onions. Roughly slice two onions. Add butter and olive oil to a skillet over medium-high heat and add sliced onions and fresh thyme leaves. Slightly brown onions and then reduce heat to medium low. Add ½ cup of water and stir occasionally. Allow water to cook down completely. When onions become brown and jammy, they have been completely caramelized, about 40 minutes. Remove from heat.
While onions are caramelizing, cook bacon thoroughly and add to a paper towel to remove access grease. Cut into small pieces and set aside.
Preheat oven to 425 degrees F. Roll out 1 sheet of pastry dough. Add caramelized onions, leaving about a ½ inch of the perimeter bare. Top with bacon pieces, crushed walnuts, and ¼ cup of the gorgonzola cheese. Top with chopped rosemary and bake for 20 minutes.
To make the balsamic glaze, combine balsamic vinegar and brown sugar in a small sauce pan and bring to a boil. Reduce heat to medium low and simmer until glaze thickens enough to coat the back of a spoon. Remove from heat and allow it to cool. (as it cools, it will continue to thicken)
Garnish puff pastry with balsamic glaze, additional gorgonzola, and fresh rosemary and thyme leaves. Add a dash of red pepper for a little kick, optional.