How to Make It
Preheat the oven to 500°. Set a pizza stone in the bottom of the oven and heat for at least 30 minutes.
Meanwhile, in a medium saucepan, melt the butter. Add the onion, cover and cook over moderately low heat, stirring occasionally, until softened but not browned, about 10 minutes. Add the water when the pan gets dry. Add the vinegar, transfer the onion to a bowl and season with salt and pepper. In a medium bowl, season the ricotta with salt and pepper.
In another medium bowl, whisk the 2 tablespoons of olive oil with the lemon juice. Add the frisée and season with salt and pepper.
On a lightly floured work surface, roll or stretch one ball of dough into a 14-inch round. Transfer the dough to a lightly floured pizza peel or inverted baking sheet and brush the edge with olive oil. Spread half of the ricotta on the dough, leaving a 1-inch border. Top with half each of the onion, Taleggio and pine nuts. Slide the pizza onto the preheated stone and bake for 5 to 6 minutes, until golden and bubbling. Drizzle lightly with truffle oil, cut into wedges and serve at once with frisée salad on the side. Repeat with the remaining ingredients to make the second pizza and serve hot, with frisée salad.