Step 1Season the chicken livers with salt and pepper on each side. Heat a large saute pan over high heat for 2 minutes. Swirl the olive oil into the pan and wait another minute. Place the livers in the pan without crowding them (you may have to do this in batches). Sear the livers on the first side for a minute or two until they are nicely caramelized. Turn them over and cook 1 more minute, until they are just medium rare. Transfer them to a platter or baking sheet.
Step 2Return the pan to the stove, lower the heat to medium and add the pancetta. Cook about 2 to 4 minutes, stirring often until the pancetta is just starting to become crisp.
Step 3Add the onion and thyme, season with salt and pepper and cook an extra 2 to 3 minutes, until the pancetta is crispy but still tender and the onion is translucent and just starting to color. Transfer the onion and pancetta to a platter or baking sheet to cool.
Step 4Chop one-third of the livers and add them to a large bowl with one-third of the onion. Place the rest of the onion, pancetta and liver in the bowl of a food processor.
Step 5Return the pan to the stove over low heat and add the balsamic vinegar. Reduce the vinegar to a glaze, about 1 to 2 minutes, and then pour it into the food processor, using a rubber spatula to scrape all of it in. Puree the livers and then add the butter little by little, pulsing all the time until the butter is completely incorporated.
Step 6Transfer the puree to the large bowl and fold in the chopped liver and remaining onion and pancetta. Test for seasoning and adjust with salt, pepper and the sherry vinegar, if using. Makes about 1 1/4 cups.
Step 1Heat the oven to 375 degrees. Place a sheet of parchment paper on a sheet pan. Arrange the pancetta on the paper and top with another sheet of parchment and then another baking sheet (this will keep the pancetta flat as it bakes). Bake the pancetta 15 to 20 minutes, until crispy. When cool, break the rounds into thirds.
Step 2Slice the baguette on the diagonal into 12 (one-fourth-inch-thick) slices (there will probably be bread left over). Brush both sides of each slice generously with olive oil, about one-fourth cup in all. Arrange the slices on a baking sheet and bake them 10 to 14 minutes, until golden and crispy but still tender in the center.
Step 3Combine the frisee, green onions, parsley leaves and chopped parsley. Dress with a splash of sherry vinegar, a good drizzle of olive oil, salt and pepper.
Step 4Spread the chicken liver mixture on each crostino and top with a piece of pancetta. Arrange the frisee on a platter and then nestle half the crostini among the salad ingredients. Top with a little more salad and prop the remaining crostini on the first six.