Heat 1 tablespoon of olive oil in a large skillet over medium-high heat.
Stir in the sliced onions and cook, stirring constantly, for 10 minutes.
Reduce heat to medium-low, add salt, sugar, and sherry.
Cook on medium-low for 25-30 minutes or until caramelized, stirring regularly. Turn off the heat and cool for 10 minutes. Meanwhile, bake the baguette slices.
Heat the oven to 400°F. Line a baking sheet with parchment paper and place the baguette slices on top. Brush the slices with the remaining olive oil. Bake for 6-8 minutes, just until the tops and edges are slightly crispy.
Assemble the appetizers: Spread goat cheese over the tops of each baguette slice, top with some caramelized onions, then garnish with rosemary.