Julienne 4 cups (1L) of onions. Sauté in 1 teaspoon olive oil until golden, about 10 minutes. Stir in rosemary and pears. Divide mixture in half and set aside.
Measure out 1/2 cup lukewarm water. Stir in sugar until dissolved. Sprinkle yeast over top and let sit until foamy, about 10 minutes. Then, stir until smooth. In a bowl, stir 3 cups flour with 1-1/2 teaspoons salt. Make a well in centre. Stir in yeast mixture, 2 cups water and 1 tablespoon olive oil. Mix in remaining flour, 1/2 cup at a time, until dough is too stiff to stir. Form a ball.
Sprinkle flour on counter. Place dough on top and flatten slightly. Top with half of pear mixture. Knead dough, working in pear mixture, from 8 to 10 minutes. Sprinkle flour under dough ball. Cover with greased waxed paper and a damp cloth. Let rise until doubled in size, about 1 hour.
Arrange racks on lowest level and in centre of oven. Preheat oven to 375F (190C). Grease an 11×17-inch (27×42-cm) jelly-roll pan or baking sheet. Punch down dough and place on greased pan and pat out evenly. Press remaining pear mixture into dough. Sprinkle with coarse salt. Drizzle with 1 tablespoon olive oil. Loosely cover with greased waxed paper and let rise until doubled, about 30 minutes.
Bake on bottom rack until golden, from 45 to 50 minutes. Lift one corner to check crust. It should make a hollow sound when tapped. If bottom is too pale, slide bread off pan and onto centre rack for 3 to 5 minutes.