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 chose the correct way to fix the error:
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.
Ingie looked at his wife's collection of cookbooks and sighed is a complete sentence. Although there were thousands of recipes for delicious meals, he knew ... begins the second sentence.
You are always correct when you use a period between the two complete sentences that create the comma splice.