02Make the crostini: Heat the oil in a skillet over medium-high heat. Add the onion and brown, turning frequently. When it begins to soften, season generously with salt and pepper; reduce heat to medium. Continue cooking for about 5 minutes, until nicely caramelized. Add the rosemary and transfer to a bowl to cool to room temperature.03Heat the oven to 400 degrees. Put the bread in the toaster until lightly browned, then lay the slices on a baking sheet. Spread about 1/2 ounce Gorgonzola on each toast, then top with the onion mixture and 3 or 4 walnut halves.04Bake on the top shelf of the oven until bubbling and lightly browned, 5 to 7 minutes. Cut into wedges if desired.05Assemble the salad: Put the greens and chopped celery in a low wide salad bowl. Just before serving, lightly sprinkle with salt and pepper, then toss with half the vinaigrette, just coating the leaves. Peel, core and slice the pears. Dress the slices with the rest of the vinaigrette in a separate bowl, spoon the pears over the salad, and serve with the warm crostini on the side.