Zuppa di cipolle gratinata

In a large, heavy-bottomed pot or Dutch oven, melt the unsalted butter with the extra-virgin olive oil over medium-low heat.

Add the thinly sliced Yellow onions and Fresh thyme sprigs. Cook slowly, stirring occasionally, for 45-60 minutes until the Yellow onions are deeply caramelized to a rich golden-brown color and very tender. This step is crucial for flavor development.

Sprinkle the 00 flour over the caramelized Yellow onions and stir well, cooking for 2 minutes to toast the flour.