Use the dutch oven technique here
to caramelize your onions and let it create a deep, brown fond.
Deglaze with Worcestershire sauce and sherry, reduce till syrupy.
Add stock, water, and herbs, and bring to a boil, then lower heat to simmer, covered for about half an hour.
Taste and adjust seasoning. You may even want to add a bit more boiling water, you go ahead.
Toast to brown and dry your baguette rounds (dry is important so they don’t fall apart in the bowl right away).
Usual method: hot soup in French onion soup bowls, good layer of grated mixed cheeses.
Into the oven under the broiler till you reach how you like it. Remember those handles get hot!