In a large bowl, whisk the flour, salt, and yeast together. Stir in the water until a shaggy dough forms, then put a clean kitchen towel over the bowl and set aside for 20 minutes to allow the flour to absorb the water a bit more.
Knead the dough on a lightly-floured counter until the dough is smooth to the touch, 5 to 7 minutes. (Alternatively, knead in a stand mixer with the dough hook attachment for about 4 minutes.)
Lightly coat a large bowl with olive oil and put the dough on top. Cover with a lid or plastic wrap and refrigerate overnight.
The next day, remove the dough from the refrigerator and let sit for 1 to 2 hours. Dust a counter with flour and put the dough on top. Divide into 4 equal pieces. One at a time, cup the pieces in your hands and tuck under the sides until you have formed a smooth ball. Place the balls on a lightly oiled pan, leaving enough space for them to rise without sticking together.
Cover the dough loosely with a kitchen towel and set aside until puffed, leaving a light indentation if pressed, 2 to 4 hours. Or you can refrigerate the dough overnight (first cover with plastic wrap that has been lightly oiled so it does not stick to the dough). If refrigerating, take the dough out of the refrigerator 2 hours before baking.
While the dough comes to temperature, prepare the toppings.
Heat 1 tbsp. olive oil in a heavy bottom pan and add garlic and chili flakes. Cook one minute until sizzling but not browned. Add sliced delicata squash and 1/2 tsp. salt. Cook until squash is soft and beginning to brown. Remove from heat and place in bowl until ready to use.
Add sliced onions, 1 tbsp. olive oil, and a pinch of salt to a blender and puree. Add cream or mascarpone and blend until smooth. Refrigerate until ready to use.
30 minutes before baking, arrange the center rungs of the oven with a pizza stone or baking steel. Preheat the oven to its maximum temperature (500°-550°F).
To shape each pizza, on a countertop dusted with flour pat each dough portion into a circle using your fingertips. Place the palm of one hand in the center and gently but firmly press down. At the same time, with the other hand, pull the dough outward while rotating it clockwise to form a flat circle with a slightly raised edge (this is the cornicione in Neapolitan-pizza speak).
Slide the dough onto a piece of parchment paper and top first with a thick even layer of the onion cream sauce. Then top with a layer of cooked squash. Slide onto hot pizza stone and cook for 6 to 10 minutes until crisp and the top is bubbling.
Remove from oven and drizzle with olive oil and sprinkle toasted walnuts on top, slice and serve.