Line a large baking sheet with parchment, and set aside.

Heat a medium skillet over low heat. Add the olive oil and sliced onions. Stir the onions to coat with oil, then allow them to cook for 30 to 40 minutes. Stir occasionally until the onions begin to soften and caramelize. They’ll turn amber in color and sweeten in flavor. Remove from heat, and set aside.

While the onions cook, preheat the oven to 400°F, and remove the puff pastry from the freezer to thaw. Once the puff pastry has thawed according to the package directions, transfer it to a lightly floured surface. Roll it out to a rectangle about 9 x 12 inches in size. Transfer it to the prepared baking sheet.

Sprinkle the goat cheese crumbles over the puff pastry leaving about 1 inch around the edges. If using a softened goat cheese, spread it with a spatula. Top the goat cheese with fresh thyme, then add the caramelized onions.

Bake for 15 to 20 minutes or until the puff pastry is golden brown. Remove from the oven, slice into squares, and serve warm.

Store leftovers in the refrigerator for up to 3 days.