Slice the bread into 1/4-inch thick slices, cutting the boule in half first. Lightly brush each piece of bread with olive oil, on both sides, before placing onto a cookie sheet and toasting lightly in the oven. Toast both sides evenly, turning halfway through. Remove from the oven and rub each piece of toast or bruschetta with the garlic, to flavor the bread. Place the bruschetti near the oven to keep warm while you make the livers.
Heat the remaining olive oil in a large skillet over medium heat. Add the cleaned livers to the pan and sear over high heat. Try not to shake the pan too much, but rather allow the livers to caramelize and brown before turning to cook the second side. Cook the livers in batches if necessary, as overcrowding the skillet will result in steamed, and not seared, livers. As the liver is turned on the other side to brown, add the shallots and cook for 2 minutes, being careful not to burn the shallots. Season with salt and pepper, tasting as you go. Add the sugar to the pan and coat the livers evenly, before adding the vinegar carefully, to avoid splattering of the caramelized sugar. Turn the heat down slightly so that the vinegar will reduce to a glossy glaze. Serve the livers immediately on the toasted bruschetti.