From the blog For Love of the Table
1 medium sweet potato—about 12 oz. (Beauregard, Jewel & Garnet are all good choices)
Salt, Pepper & Nutmeg
2 T. Olive oil, plus more for brushing
1 small red onion (about 6 oz.), cut into a 1/4-inch dice
pinch of red pepper flakes
1 fat clove of garlic, finely minced
1 bunch Red Russian kale (Green Kale or Tuscan Kale will also work), stems stripped away and discarded
Pizza dough (see below)
3 1/2 to 4 oz. goat cheese, coarsely crumbled
3/4 to 1 oz. (1/4 to 1/3 cup) finely grated Pecorino
Prick the sweet potato in several places. Place on a small baking sheet and transfer to a 400° oven. Bake until tender and oozing sugary syrup—about 40 minutes to an hour. When cool enough to handle, remove the skin and discard. Mash the flesh with a fork and season to taste with salt, pepper and nutmeg. You should have about 3/4 cup of sweet potato purée (see note). Set aside. (Sweet potatoes may be prepared ahead...or leftovers may be used.)
While the sweet potatoes roast, cook the onions and kale: Bring a large pot of salted water to a boil. Add the kale and cook until tender—about 7 to 10 minutes. Drain and spread on a baking sheet to cool. When cool, squeeze firmly to remove as much water as possible. Chop coarsely and set aside.
Heat 2 T. of olive oil in a sauté pan set over medium heat. Add the onion, along with a pinch a salt and the pepper flakes and sweat until the onion is very tender and beginning to caramelize—15 minutes or so—regulating the heat as necessary to keep the onion from burning. Add the garlic and continue to cook until fragrant—a minute or two. Add the kale, toss with the onion-garlic mixture and cook until the kale has given up any remaining excess water and has begun to sizzle in the olive oil (add a bit more if the pan seems dry). Set aside.
Build the pizza: Roll the rested dough out into a 11- to 12-inch round (the dough will continue to stretch another inch or so in diameter when you spread the sweet potatoes) and transfer to a baking sheet, pizza pan or pizza peel that has been dusted with flour or cornmeal. Brush the dough with a little olive oil. Spread the sweet potato purée over the dough, leaving a 1/2-inch border. Spread the kale mixture over the sweet potato and crumble the goat cheese evenly over the kale. Scatter the Pecorino evenly over all.
Bake the pizza: If using a pizza pan or baking sheet, place the pizza in the pan on a pre-heated pizza stone in a pre-heated 450° to 500° oven. Bake until the crust is golden brown on the bottom and the cheese is tinged with golden brown, about 12 to 15 minutes. To insure a crisp crust, slide the pizza off of the pan and onto the pizza stone as soon as the crust is set (after 4 or 5 minutes).
If using a peel, slide the pizza directly onto the preheated baking stone. Bake until the crust is golden brown on the bottom and the cheese is tinged a golden brown color—about 8 to 12 minutes.
When the pizza is done, transfer to a cutting board and cut into wedges and serve.
Note (added November 2015): I have noticed this year that the sweet potatoes have tended to be a bit drier than usual. If you find yourself with an unmanageably stiff and dry sweet potato purée, drizzle in a bit of olive oil...or milk...to let it out to a more spreadable consistency.
http://www.forloveofthetable.com/2013/11/pizza-with-sweet-potato-kale-goat.html