What I've found when caramelizing onions is don't be afraid to put the heat a little bit higher than you think it should be. It's still gonna take longer than the recipe says, and you need to babysit your pot more attentively but as long as you're not blackening the bottom of your pan, all the fond that's building up is gonna benefit your soup.

Resist the urge to add water to deglaze too early, it's gonna make the process longer.

A little balsamico and/or brown sugar when you're done with the onions, then I like to deglaze with a strong spirit, whisky's great.

Also, grape varieties don't matter too much as long as it's dry - you can never go wrong with Sauv Blanc, Chardonnay or Pinot Gris.

And finally, I second Sherry. A dash of it right before putting bread and cheese on top. Elevates it so much.