Looking for a frosting that tastes like summer? This Key Lime Marshmallow Buttercream is light, fluffy, and bursting with fresh key lime flavor. It starts with my Marshmallow Buttercream and adds bright key lime juice and zest for a sweet and tangy frosting. It is perfect for filling Key Lime Sandwich Cookies and just as tasty on cakes, cupcakes, cookies, and bars.
Ingredients & Substitutions
- Butter: Unsalted butter gives the frosting a rich, creamy base. Make sure it is at room temperature so it blends smoothly with the cream cheese. If using salted butter, you may want to lessen or leave out the salt.
- Marshmallow Creme: Marshmallow creme (also called marshmallow fluff) gives this buttercream its light, fluffy texture and sweet marshmallow flavor. Store-bought works great, or you can make my Homemade Marshmallow Fluff for an extra special touch.
- Cream Cheese: Softened cream cheese adds a slight tang that balances the sweetness and pairs perfectly with the key lime. Be sure it is at room temperature for the smoothest frosting.
- Confectioners’ Sugar: Confectioners’ sugar sweetens the frosting while keeping it silky smooth. Add it gradually so it mixes in easily.
- Key Lime Juice: Fresh key lime juice gives the frosting its bright, citrusy flavor. Start with 1 tablespoon, then add more to taste. If you can’t find key limes, regular lime juice will work, but the flavor will be slightly different.
- Key Lime Zest: Don’t skip the zest! It adds fresh lime flavor without thinning the frosting. If using regular limes, simply substitute lime zest.
- Kosher Salt: Just a pinch balances the sweetness and helps the citrus flavor shine.
- Vanilla Extract: A little vanilla rounds out all of the flavors and complements both the marshmallow and key lime.
Tips for the Best Key Lime Marshmallow Buttercream
- Use room temperature ingredients. Softened butter and cream cheese blend more easily, creating a smooth, creamy frosting without lumps.
- Add the key lime juice slowly. Start with 1 tablespoon, then add more if you want a stronger citrus flavor. Adding too much at once can make the frosting softer.
- Don’t skip the zest. Key lime zest adds a big pop of fresh lime flavor and helps balance the sweetness of the marshmallow creme.
- Whip the frosting at the end. After all the ingredients are combined, beating the frosting for a minute or two makes it light, fluffy, and easy to spread or pipe.
- Chill if needed. If your frosting feels too soft, place it in the refrigerator for a short time before using.
How to Use Key Lime Marshmallow Buttercream
This fluffy frosting is delicious in so many desserts! My favorite way to use it is between two Key Lime Cookies to make sweet, citrusy sandwich cookies. It is also perfect for:
- Filling or frosting cupcakes (Have you tried my Key Lime Cupcakes, yet?)
- Spreading between cake layers or over a sheet cake
- Adding a creamy layer to brownies, bars, or cookies
Because this buttercream is light and fluffy, it works especially well anywhere you want a sweet frosting with a bright key lime flavor.
FAQs
Can I use regular limes instead of key limes?
Yes! Regular limes work well in this frosting. Key limes have a slightly sweeter, more floral flavor, but regular limes will still give the buttercream a bright, fresh citrus taste.
Can I use homemade marshmallow fluff?
Absolutely! Homemade marshmallow fluff works beautifully in this buttercream and gives it a delicious homemade flavor. You can use it in the same amount as store-bought marshmallow creme.
Does Key Lime Marshmallow Buttercream need to be refrigerated?
Because this frosting contains cream cheese, it should be refrigerated if you are not using it right away. For the best texture, let it sit at room temperature for a bit before frosting so it becomes soft and easy to spread.
Can I make this buttercream ahead of time?
Yes! You can make this buttercream ahead of time and store it in an airtight container in the refrigerator for up to 5 days. Let it come to room temperature, then mix it briefly before using to bring back its light, fluffy texture.
How to Store Key Lime Marshmallow Buttercream
Because this frosting contains cream cheese, store any leftover Key Lime Marshmallow Buttercream in an airtight container in the refrigerator. It will keep well for up to 5 days.
Before using, let the frosting sit at room temperature until softened. You can also mix it briefly with a mixer to bring back its light, fluffy texture.
Can I Freeze Key Lime Marshmallow Buttercream?
Yes! This buttercream freezes well. Store it in a freezer-safe container for up to 2 months. When you are ready to use it, thaw it overnight in the refrigerator, then let it come to room temperature. Give it a quick mix before frosting to make it smooth and fluffy again.
Key Lime Marshmallow Buttercream
Ingredients
- ½ cup (1 stick / 113 g) unsalted butter, room temperature
- 1 jar (7 ounces) marshmallow creme (marshmallow fluff)
- 4 ounces cream cheese, room temperature
- 4 cups (500 g) confectioners' sugar
- 1 to 2 tablespoons key lime juice
- 1 teaspoon key lime zest
- 1 pinch kosher salt
- ½ teaspoon vanilla extract
Instructions
- In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and cream cheese until smooth and creamy, about 2 minutes.
- Add the marshmallow creme and mix until fully incorporated, scraping down the sides of the bowl as needed.
- With the mixer on low speed, gradually add the confectioners’ sugar, mixing until smooth and combined.
- Add 1 tablespoon of the key lime juice, the key lime zest, kosher salt, and vanilla extract. Mix until fully incorporated.
- Taste the frosting and add the remaining tablespoon of key lime juice, if desired, until it reaches your preferred balance of sweetness and citrus flavor.
- Increase the mixer speed to medium-high and beat for 1 to 2 minutes, or until the frosting is light and fluffy.
- Use immediately to frost cakes, cupcakes, cookies, or bars.
Did you make this recipe?
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