All of the flavors of your favorite soup are wrapped up in puff pastry for this delicious appetizer. It is a perfect make ahead snack for your next party.
In a skillet over medium-low heat, melt butter. Add onions, bay leaf and pinch of salt and stir to combine. Continue to cook over low heat as onions slowly cook and caramelize. To do it right, it will take a long time but it is low maintenance. Just give it a stir every so often and let them slowly develop an nice golden color.
Once they are completely caramelized, stir in the garlic and thyme and remove from the heat. Allow to cool to room temperature.
Roll out the puff pastry to about ¼-inch thick. Spread onions over puff pastry, leaving a small border on either side. Sprinkle with shredded gruyere.
Roll one side toward the center of the dough. Then repeat with the second. Wrap tightly with plastic wrap and refrigerate for at least a half hour.
Preheat oven to 400°F and line two baking sheets with parchment paper or silicone mats.
Cut stuffed puff pastry dough into 1/3-inch slices and carefully transfer to baking sheets. Bake for 15-20 minutes or until puffed and golden.