Begin by gently steeping saffron threads in lukewarm water for about 5 minutes to release their vibrant color and flavor.

In a large mixing bowl, combine the saffron-infused water with whole milk, instant yeast, and 1 cup of flour. Let the mixture rest for 20 minutes to allow the yeast to activate.

Incorporate the remaining flour, egg, olive oil, and kosher salt, mixing until a smooth dough forms. Cover with plastic wrap and refrigerate overnight.

In a skillet, heat olive oil over medium heat and add sliced yellow onions with a pinch of salt. Sauté for 8 minutes.

Lower the heat and continue cooking for an additional 30 to 40 minutes until the onions are golden brown and caramelized.

In a food processor, combine pistachios, cilantro, olives, garlic, extra virgin olive oil, and salt. Pulse until it forms a coarse paste.

On a floured surface, roll the chilled dough into a rectangle. Spread pesto over the dough, followed by the sautéed onions, Gruyere cheese, and prosciutto.

Roll the dough into a cylinder, shape it into a wreath, and let it rise for 45 minutes.

Preheat your oven to 400°F (200°C). Brush the wreath with egg wash and cut slits on top.

Transfer to a preheated baking stone and bake for 25 to 35 minutes until golden brown. Let cool for 10 minutes before slicing.