Put the olive oil in a large skillet and place over high heat for 1 minute. Add the onions, reduce the heat to medium and then add the sugar, salt, white pepper, ground sage, chopped fresh sage and sauté, stirring frequently, until tender and nice and caramelized, about 15 to 20 minutes. Remove from heat and place the onions in a large mixing bowl. Allow to cool slightly.
Whisk eggs and cream together and mix into the onions. Put the sheets of puff pastry onto baking sheets, dock with a fork, and spread the onion mixture evenly onto the surface. Place in the oven 20 to 30 minutes, until bottom is golden brown. Remove from oven, let cool 15 minutes and slice into 2-inch squares. Arrange on a decorative platter and garnish with fresh sage leaves.