For cooking vegetables.
Well, for boiling or steaming vegetables.
For cooking your grains perfectly.
For hosting a party.
Running out is not an option. Heather from Chickabug has plenty more tips for party planning, cooking and decorating.
For vegan baking.
You may have to experiment a little bit to figure out which replacement is best for particular recipes, but here’s a good starter guide on egg substitutions.
For knowing what kind of onion to use.
You won’t ruin a recipe by using a sweet onion when a red onion would have been better, but different onions have different characteristics—some are milder, some are sweeter, etc.—so it’s good to know the difference.