Preheat oven to 400 degrees F. Arrange butternut squash and onions on a baking sheet. Drizzle with olive oil and season with salt and pepper. Roast in preheated oven for about 40-45 minutes, until soft and starting to caramelize. Set aside to cool. Reduce oven temperature to 350 degrees F.
In a medium bowl, beat together eggs until combined. Add milk and whipping cream, beating until light and airy. Stir in sage leaves and season with salt and freshly ground pepper, to taste.
Fill the blind baked pie crust with the butternut squash and caramelized onion mixture. Top with gruyere cheese. Pour egg mixture over the top.
Place quiche in 350 degree F oven. Bake until center is just set, about 40-45 minutes, rotating halfway through. (If crust is starting to get too brown, cover with foil or a pie crust shield to prevent from burning). Remove from oven. Cool at least 15-20 minutes, or until room temperature before serving.
Notes
To blind bake a pie crust, roll out pie dough and place in pie dish, crimping edges if desired. Lay a sheet of parchment paper over the top of the dough (the parchment should line the bottom and sides, and extend up past the sides of the dough for removal). Fill parchment with pie weights (you can use dried beans or rice if you don't have any). Bake in a preheated oven (at the temperature recommended for the pie crust you are using) until edges are cooked. Remove from the oven and remove the parchment and pie weights. Prink bottom and edges with a fork a few times (to prevent it from puffing up). Return the oven and continue to bake a little longer until bottom looks cooked through, then remove from oven and let cool slightly before filling with quiche filling.
Recipe by Wright Family Table at https://www.wrightfamilytable.com/autumn-butternut-squash-quiche/