If using fresh yeast, mix water and yeast together in the bowl of a stand mixer until yeast is dissolved. If using active dry yeast, mix water and yeast in the bowl and let sit until the yeast is foamy, about 5 minutes.
Using a dough hook, beat in flour and salt and mix until smooth, slightly elastic dough forms, 2 to 3 minutes; do not knead.
Place dough in an oiled bowl, turn dough to coat, cover loosely with plastic and refrigerate for at least 24 hours, and up to 48 hours to proof.
When you are ready to make pizza, divide dough into 4 equal pieces. Shape each piece by using the palm of your hand to rotate the dough clockwise until a tight, compact ball has formed. Turn dough over. Working from the outside in, pinch and twist the edges of the dough into the center to make a very tight ball. Put dough on a baking sheet and return to the refrigerator to rest for a least 4 hours, and up to 12 hours.
When you are ready to make pizzas, remove dough from the refrigerator and let it sit at room temperature for at least 30 minutes (take the dough out of the fridge while you preheat the pizza stone). You can let it sit out longer, as long as it doesn’t get too soft and floppy, which would make it difficult to shape; soft dough is also more likely to stick to the baking sheet or pizza peel, making it harder to slide onto the stone. If the dough gets too soft, stick it back in the fridge for 10 minutes or so to give it a chance to firm up. Shape and top as desired.
For Clam Pizza:
For the pizzas: Preheat the oven to 500°F, with a pizza stone on a rack in the top third of the oven. Let heat for 1 hour. Remove the pizza dough from the refrigerator at least 30 minutes before baking.
While the oven heats, place 1/4 cup olive oil in a large pot over medium heat. Add the onion and sauté until it is limp, about 5 minutes. Add the garlic, reduce the heat to low, and cook for 7 minutes, until the edges are golden. Add the wine and bring to a simmer. Add the clams, cover the pot, and cook until the clams start to open, about 10 minutes. As they open, transfer them to a large bowl. When all the clams are cooked, simmer the liquid in the pot until it reduces to a thick glaze, about 10 minutes. Add the cream, bring to a simmer, and reduce by a quarter, 10 to 15 minutes longer. Strain through a fine-mesh sieve into a bowl and set aside. It thickens as it cools.
Meanwhile, when the clams are cool, pluck out the meat and discard the shells.
Turn a large baking sheet upside down, or use a pizza peel. Dust the surface with flour. Form one piece of the dough into a 12-inch round and set it on the baking sheet or peel.
Working quickly, paint the entire surface of the pizza with one-fourth of the glaze. Scatter the clams over the pizza and sprinkle with chili flakes.
Jiggle the pizza gently on the pan (or peel) to make sure it is not sticking (if it is, loosen it and sprinkle a little more flour under the area where it stuck). Slide the pizza onto the hot stone, making sure to start at the stone’s back end so that the entire pizza will fit on it.
Cook the pizza for 3 minutes. Turn on the broiler. Broil the pizza until golden, crisp, and a bit blistery and charred in places, 2 to 4 minutes (watch it carefully to see that it does not burn). If you don’t have a peel, use tongs to slide the pizza onto a large platter. Drizzle with oil and scatter with one-fourth of the parsley.