1 medium yellow onion, halved and thinly sliced
1 tablespoon butter
Salt and pepper
1/2 cup balsamic vinegar
1 frozen puff pastry, thawed
2 teaspoons olive oil
4 plum tomatoes, thinly sliced
2 tablespoons mild goat cheese
1/3 cup fresh basil leaves, cut chiffonade style (long thing strips), divided
In a small pan over low heat, melt butter. Add onions and season with a pinch of salt and pepper. Use a wooden spoon to stir and break apart the slices. Cook for about 15-20 minutes until onions are slightly browned and caramelized. Remove from pan and set aside in a bowl.
Meanwhile, place balsamic vinegar in a small pot. Bring to a boil then stir and reduce heat to very low. Cook for about 10 minutes until the vinegar reduces by about half and it has turned into a glaze. Remove from heat and place in a bowl.
When you're ready to cook, preheat oven to 400. On a parchment lined baking sheet unfold the puff pastry. Use your hands to gently press down to make sure even all around. Use a sharp knife to score a border around the edge, about 1/2 inch on all sides. Don't pierce all the way through the pastry! Use a fork to poke holes throughout the center of the pastry inside the square you have drawn. Once again, don't pierce all the way through.
Drizzle with olive oil and brush all over pastry then sprinkle with a pinch of salt and pepper. Layer the caramelized onions evenly on top of pastry then top with tomato slices all over. Sprinkle tomato slices with a little salt. Top with crumbled goat cheese and then half of the basil. Place in oven and cook for about 18-22 minutes until the edges have puffed and are slightly golden brown. Remove from oven and set on serving platter. Drizzle with as much balsamic reduction as you like then cut into slices. I cut mine into about 16 slices.