In a heavy skillet, heat olive oil over medium-low heat. Add sliced onions, salt, and black pepper. Cook for 35-45 minutes until golden brown and jammy.

Preheat the oven to 400°F (200°C) and prepare a baking sheet lined with parchment paper. Roll out puff pastry into a rectangle about 1/8 inch thick.

Spread the cooled caramelized onion mixture over the pastry, leaving a half-inch border. Sprinkle with fresh thyme.

Roll the pastry tightly from the edge opposite the border. Slice the log into ½-inch rounds and arrange on the baking sheet.

Bake for 18-22 minutes or until golden brown and puffed.