1. Preheat oven to 450°. Line a cookie sheet with foil and set aside. Prepare the creamy herb sauce by combining all ingredients in a bowl and whisking together until smooth. Cover & set aside. Remove pizza dough from refrigerator and place in a covered bowl while you work.
2. Place the sweet potato slices in a bowl and drizzle lightly with olive oil. Toss, then place in a single layer on the prepared cookie sheet. Roast for no more than 10 minutes; remove from oven and set aside.
3. While the sweet potatoes are roasting, begin to caramelize the onions. Heat 2 tablespoons of olive oil in a skillet. Place onions in skillet, sprinkle with salt and saute slowly over medium heat for about 10-15 minutes, until the onions have turned a rich, caramel brown. Remove from heat and set aside.
3. Dust your hands and work surface lightly with flour. Working from the center of your ball of pizza dough, gently stretch & shape it to the desired size (since I don't have a pizza stone or pan, I just go rustic & let it make it's only oblong shape; if you prefer round or square pizza, feel free to make those instead).
4. Brush the dough lightly with olive oil, spoon 2-3 tablespoons of the creamy herb sauce on top, then spread over the surface, leaving about 3/4? distance from the edge of the crust. Sprinkle with cheese, then add the sweet potato slices and a couple tablespoons of caramelized onions. Bake for 10-15 minutes, until crust begins to turn golden brown. Remove from oven and sprinkle with chopped spinach and more onions (more cheese, too, if you like).
5. Allow to cool for about 5 minutes before cutting. Using a pizza wheel or sharp knife, cut into 6-8 pieces (depending on size of pizza). Serve with a nice salad and a small side of creamy herb sauce, and enjoy!