In a heavy 2-quart saucepan mix together the chicken broth, half-and-half, onion, salt, white pepper & hot pepper sauce.
Several hours before serving, peel the avocado, then pit & cut it into 1-inch pieces. Place in a medium, nonreactive bowl. sprinkle with lemon juice, then cover with plastic wrap & refrigerate until ready to use.
Just before serving, put 1/4 cup of the chicken broth mixture in a blender.
Bring the rest of the broth mixture to a boil in the 2-quart saucepan, then reduce heat to low.
Add avocado to the blender & process until smooth, then pass this mixture through a coarse-mesh sieve.
Add the sieved avocado mixture to the simmering broth & heat, BUT DO NOT LET IT COME TO A BOIL. Salt to taste.
Serve immediately with croutons (if using) on the side, or make it several hours ahead of time, cover with plastic wrap & let it cool, then chill completely before serving.