Review the original item:
Ingie looked at his wife's collection of cookbooks and
sighed,
although there were thousands of recipes for delicious meals, he
knew that Valerie would want to order another pepperoni and mushroom pizza
for dinner.
You wanted to fix it this way:
Ingie looked at his wife's collection of cookbooks and
sighed although there were thousands of recipes
for delicious meals, he knew that Valerie would want to order another pepperoni
and mushroom pizza for dinner.
To delete the comma between sighed and although would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two complete sentences joined with no punctuation whatsoever. Ingie looked at his wife's collection of cookbooks ... begins the first sentence. Although there were thousands of recipes for delicious meals, he knew ... starts the second sentence.
The spot between sighed and although needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.