The cold sweat that drips down your neck when you realize you're missing an ingredient, and the cake batter is halfway finished, is real. You have guests scheduled to arrive in mere hours, nay, minutes. Do you rush to the store and grab a bundt cake shelled in plastic? Do you skip dessert altogether, assuming the party will accept your bashful "Dessert? Oh no, not here. I'm trying to slim down." NEVER ACCEPT DEFEAT. Below I offer my quick list of substitutions should you find yourself in pastry-panic. Keep calm and bake on.

Cake flour

What is cake flour? Cake flour is a different subset of wheat. It has a lower protein content than the wheat we find in regular all-purpose flour (7-8% VS 10-12%), and it is ground more finely. That protein becomes gluten as the flour reacts with liquid around it. Cakes need less gluten to stay together than bread. Swap out two tablespoons of your all purpose flour for two tablespoons of corn starch. That substitution will lower the protein content and increase the starch ratio (eliminating some gluten formation and creating a light and soft cake).

Sugar, sugar, sugar

If a recipe calls for Superfine Sugar, simply run granulated sugar in the food processor for 30 seconds (in short bursts). Beware of spinning it too long, the heat from the motor can start molecular breakdown (caramelization).
Powdered sugar is nothing more than granulated sugar pulverized with cornstarch. To mimic this, buzz one cup of granulated sugar and one teaspoon of cornstarch together in a spice mill. Why the spice mill? The smaller volume of the container on a spice mill means that the grains of sugar will come in contact with the spinning blades more often, resulting in more structural damage (a good thing here). Food processors are too vacuous for this event.
When you are in need of brown sugar, look no further than the bottle of molasses you've kept in the pantry since you baked gingerbread once, 15 years ago. Mix one cup of granulated sugar with one teaspoon of molasses in your food processor.

Buttermilk

Ever found yourself troubled over buttermilk? Buttermilk tends to be an ingredient that we don’t have on hand, but when we need it, we really need it! As with other ingredients, understanding what buttermilk really is will help us make a substitution. Buttermilk, traditionally, is the liquid left behind after churning butter out of cream. Things to remember about buttermilk: it is tart and it is thick. What makes it tart? Acid, specifically lactic acid produced by bacteria fermenting lactose, the sugar found in dairy products.
So, if we’re looking to replace a thick, slightly tart, acidic dairy product, add a touch of vinegar or lemon juice to whole milk. The lemon juice will simultaneously lower the pH of the milk (acidification) while it begins to unfold casein (the milk protein) which thickens the liquid. For one cup of buttermilk, let one cup of whole milk stand with one teaspoon of vinegar or lemon juice for five minutes.

Leavening

There is one major chemical we use to help give lift to our baked goods. Sodium Bicarbonate, also known as baking soda. But what about baking powder? Baking powder is nothing more than sodium bicarbonate (baking soda) with tartaric acid (also known as cream of tartar). Sodium bicarbonate is a weak base, and cream of tartar is an acid. When they react, we see the release of carbon dioxide. This is often demonstrated by pouring vinegar over baking soda (a grade school experiment of the highest order). But baking powder is perfect in baked goods that don’t have an additional acid content. We need acid to react to the base in order to release carbon dioxide. Plain water will dissolve the tartaric acid in baking powder, releasing it to react freely with the sodium bicarbonate and freeing carbon dioxide, giving lift to cakes and cookies. If you run out of baking powder use this instead: for one teaspoon powder, swap in 1/4 teaspoon baking soda plus 1/2 tsp cream of tartar

Chocolate

Those squares of unsweetened chocolate tend to reach old age in the back of a cupboard. So, when you are in the middle of baking brownies and find yourself without a square to save the day, grab for the cocoa powder instead. For one ounce of unsweetened chocolate mix three tablespoons cocoa powder with one tablespoon butter, margarine, or oil. Unsweetened chocolate is cocoa solids and cocoa butter, without any sugar. Cocoa powder is a desiccated powder of cocoa solids. Simply add fat and you're ready to rock.

Egg

When it comes to replacing eggs we have to mimic a unique combination of protein, fat, and water. The chemical structure of eggs can provide lift, heft, and binding all in one but most replacements can cover only one or two of those traits. For my MisCake I wanted to replace heft (lift I had in spades from the buttermilk and baking powder). Considering my need for body in the cake, banana was an excellent replacement. Water, fat, protein, and mass!

Vanilla

Vanilla is truly a flavor powerhouse in baking, but it isn’t the only aromatic alcohol. Indeed, vanilla is made by steeping whole beans in alcohol until the liquid is suffused with its floral notes. When you’ve tapped the end of your vanilla bottle mid-recipe, simply raid your liquor cabinet. Surely you have some rum, whiskey, rye, bourbon, or even tequila hanging around. These dark alcohols are full of flavor compounds not dissimilar from our stalwart vanilla extract.

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