How To Thicken Frosting For Cakes And Cookies

When baking, it's always wise to start with a thicker frosting and thin it out as needed, but a thick frosting comes in handy in various baking projects and applications. To build a structurally-sound layer cake, you'll want to use a thick, firmer buttercream between your cake layers, giving the cake height and keeping it level. When decorating cookies, a firm royal icing is crucial to piping elegant, clean designs and fine lines.

While it's relatively easy to thin out your frosting—a bit of water, milk, or cream should do the trick—regaining body and thickness in your frosting is slightly more challenging. But don't worry, it's not impossible. Frosting can go wrong for many reasons, but we're here best practices to return to fluffy frosting perfection.

Some of our techniques for thickening frosting call for added ingredients, like powdered sugar, while others only require time. We're giving you the complete rundown on thickening frosting in a pinch, whether you're working with buttercream or royal icing. Keep these tricks in your back pocket for future baking mishaps.

When you are frosting a cake, it's crucial to work with buttercream that's reached the perfect consistency. If your frosting is too runny, it'll melt and slide all over the cake. If it's too thick, it won't spread easily. Think of building and frosting your layer cake as a construction process. You'll want to start by forming a solid base structure, then work from there. When making a cake, we start with a thick, firm buttercream, then as we move into the decoration, we thin our frosting out with a little bit of heavy cream to make it more spreadable.

How to Fix Thin Buttercream

If you're starting with a thin and runny frosting, don't fret: You can come back from this. There are a few different ways to thicken your frosting to ensure that your cake is sturdy, clean, and polished.

1. Chill and wait

Allow your frosting to sit in the fridge, covered with saran wrap, for 2 hours—this will help your frosting firm up.

2. Add powdered sugar

If the frosting has not reached your desired thickness after chilling, add a few tablespoons of sifted powdered sugar to help your buttercream stiffen.

If you're making royal icing, often used for decorating cookies, mixing to the right consistency is key to achieving clean, pretty lines and decorative features. Icing with a flooding consistency, a looser icing used to fill in large surfaces differs from piping icing used for intricate designs because it is much stiffer.

Always start with a firmer icing, then gradually add water to make it more liquid. Add water—a few tablespoons at a time—until the icing reaches a spreadable consistency to achieve a flooding-consistency icing.

How to Fix Thin Royal Icing

If you accidentally added too much water at the onset, making your icing far too runny for the piping bag, and need to make the icing firmer rather than looser, there are solutions for this problem too.

1. Add powdered sugar

To thicken your royal icing, add more sifted powdered sugar—a couple of tablespoons at a time—until the icing reaches your desired consistency.

2. Add corn starch

If you want to thicken your royal icing without adding additional sugar, you can add a minimal amount of corn starch (less than a teaspoon) to help your icing thicken up.

3. Let it rest

Allowing icing time to rest and chill in the fridge can also help it gain more body—if it's not already in the piping bag, be sure to cover the bowl with saran wrap, so the icing doesn't form a crust.