Caramelize the Onions: Heat 1 tablespoon of olive oil in a pan over medium heat. Add the sliced onions and sauté until tender, about 10-15 minutes.
Slow Cook the Onions: Reduce the heat slightly, add 1/4 cup water, cover, and cook the onions for an additional 50 minutes until they turn a deep golden brown, stirring every 10 minutes for the first 30 minutes, then every 5 minutes thereafter. Add more water as needed to prevent drying.
Roast the Pumpkin: Preheat the oven to 350°F (180°C). Toss the pumpkin or butternut squash with 1 tablespoon of olive oil, salt, and pepper. Spread evenly on a baking sheet and roast until tender, about 30-40 minutes. Set aside once done.
Prepare the Phyllo Crust: Increase the oven temperature to 375°F (190°C). Brush a sheet of phyllo dough with olive oil and place it into the bottom of a greased 9-inch pie dish or springform pan, letting the edges hang over the side. Repeat with the remaining phyllo sheets, layering them on top of each other.
Assemble the Quiche: In a large mixing bowl, combine the caramelized onions, roasted pumpkin, eggs, half and half, gorgonzola, and sage. Pour the mixture into the prepared phyllo crust.
Bake: Bake the quiche in the preheated oven for 25-45 minutes, or until the crust is golden brown and the center is set. Let cool slightly before serving.