Place a sheet pan on the oven’s lowest rack and heat the oven to 450 degrees. In a liquid measuring cup or small bowl, stir together the heavy cream, Parmesan, lemon juice, garlic, nutmeg (if using), and red-pepper flakes. Season to taste with salt; set aside. In a medium bowl, sprinkle the kale with the olive oil and a big pinch of salt; squeeze with your hands until wilted.
Place a kitchen towel on a work surface, then place an upside-down sheet pan or cutting board on the towel. (This will serve as your pizza peel; the towel stabilizes the setup as you roll the dough.) Line the upside-down sheet pan with parchment paper, lightly grease the parchment paper with olive oil and place the dough on top. Stretch or roll the dough on the parchment into a 9-by-13-inch rectangle. If the dough shrinks, let it rest a few minutes before continuing.
Sprinkle the mozzarella over the dough, then add the kale in an even layer. Spoon the heavy cream over the kale, then top with the shallots.
Remove the heated sheet pan from the oven and carefully slide the parchment with the dough onto the hot baking sheet. Cook until the cheese and the crust is golden brown, 14 to 16 minutes.
Use tongs to transfer the pizza to a cooling rack, leaving the parchment behind. Let sit for a few minutes to crisp and cool slightly before cutting and serving.