Begin by heating a large skillet over medium heat, adding a drizzle of olive oil along with a tablespoon of butter. Once melted, add thinly sliced yellow onions, stirring frequently for about 30 minutes until golden-brown.

After the onions have caramelized, stir in 1 cup of beef broth and 1 tablespoon of white vinegar. Allow this mixture to simmer for approximately 5 minutes.

Preheat your oven to 375°F (190°C). Unroll the crescent roll dough onto a clean surface, cut into 3x3-inch squares, and press each square into the wells of a greased mini muffin tin.

Spoon the savory onion mixture into each dough cup, filling them about ¾ full. Top with grated Gruyère cheese.

Bake for 18 to 20 minutes until the dough is puffed and golden, and the cheese is bubbly.

Let the bites cool for a few minutes, then gently pry them out and garnish with fresh thyme leaves. Serve warm.