I promise this picture will make sense. Stay with me.
I'm sure I'm the only one who has ever experienced this (*cough cough*), but sometimes I'll be well into a recipe and realize I've run out of an ingredient. For some reason, this usually happens on a Sunday afternoon, thus making a trip to the store not really an option. However, I'm lucky to have a mom who taught me some ways around this conundrum.
There are various, easy ways to substitute certain ingredients with other things when needed. The results are usually fine, though maybe not as good as the original. But, I'm all for avoiding a trip to the store for a single item, especially when I'm in a pinch. Here's a few of the emergency substitution solutions I've gathered in my years of cooking and baking:
For brown sugar, add molasses to regular granulated sugar. To make a cup of brown sugar, add 1 tablespoon of molasses to a cup of granulated sugar. If you need dark brown sugar, add 2 tablespoons. Pulse the sugar and molasses together in a food processor or just add the molasses with the other wet ingredients in the recipe.
For baking powder, combine baking soda and cream of tartar. To make a teaspoon of baking powder, combine 1/4 teaspoon of baking soda and 1/2 teaspoon of cream of tartar. Be sure to use this right away.
Dried herbs can replace fresh herbs. Just use a smaller amount. If the recipe calls for a tablespoon of fresh herbs, use 1 teaspoon of the dried herbs.
If a recipe calls for plain yogurt, sour cream can be used instead - and vice versa. I've used plain yogurt on tacos before and we could hardly tell the difference (the yogurt had a little more tang to it).
All-purpose flour can replace cornstarch when used for thickening. For 1 tablespoon of cornstarch, use 2 tablespoons of flour.
If you don't have cake flour on hand (quite the possibility), you can make it with cornstarch and regular all-purpose flour. Check out this link from Joy the Baker for a detailed how-to.
For those who don't have a bottle of wine on hand or choose not to purchase it for other reasons, wine in recipes can be replaced with broth and either vinegar or lemon juice. To make a substitution for a 1/2 cup of wine, mix 1/2 cup broth with either a teaspoon of wine vinegar or 1 teaspoon of lemon juice.
If a recipe calls for a square of unsweetened chocolate, you can mix cocoa powder and vegetable oil as a substitution. To make a substitution for a square (which is usually an ounce) of unsweetened chocolate, mix 3-4 tablespoons of cocoa powder with a tablespoon of vegetable oil.
Whole milk can replaced with a mix of evaporated milk and water. To replace a cup of whole milk in a recipe, combine 1/2 cup of evaporated milk and 1/2 cup of water. Or, if you have it, you can mix 2/3 cup of 1% milk with 1/3 cup of half-and-half; or 3/4 cup 2% milk with 1/4 cup half-and-half. (Psst... Don't tell anyone, but sometimes I just use 1% milk without anything else and it has worked fine. It may take longer to thicken if you add it to a roux, but it still works).
And if a recipe calls for buttermilk, you can use a mixture of regular milk and lemon juice or vinegar. I use this one all the time. To make a substitute for 1 cup of buttermilk, mix 1 tablespoon of lemon juice or vinegar with a cup of milk. Let it stand for about 10 minutes - this will give it time to curdle the milk and thicken. Only use this for cooking or baking - not for raw uses, like salad dressing.
And if you didn't figure it out, the buttermilk substitution is why I included the picture. It's from Charlotte's Web, when Mrs. Zuckerman gives Wilbur a buttermilk bath before going to the fair. Whenever I think of buttermilk, I almost always think of Charlotte's Web.