Place a small sauce pan over medium-high heat and add the balsamic vinegar. Bring up to a light simmer and cook for about 6-8 minutes, or until it reduces by about half and thickens up.
While the balsamic vinegar is cooking, place a medium-size skillet over medium-high heat and add EVOO. Add the onion and apples to the pan and cook for about 8-10 minutes, until the mixture starts to brown. Add the pine nuts and season with salt and pepper.
Top the toasted baguette slices with a spoonful of the onion and apple mixture and drizzle with the reduced balsamic vinegar and serve.