These Key Lime Sandwich Cookies are like a little bite of summer! I took my buttery Key Lime Cookies and paired them with a fluffy, creamy Key Lime Marshmallow Buttercream filling to create a cookie that is sweet, bright, and full of fresh citrus flavor. They are perfect for sharing, gifting, or keeping a few extra for yourself!
Ingredients & Substitutions
- Butter: Unsalted butter gives both the cookies and the buttercream a rich, creamy flavor. Make sure it is softened to room temperature so it mixes smoothly and creates the best texture.
- Confectioners’ Sugar: Also called powdered sugar, confectioners’ sugar is used in both the cookies and the filling. It helps create a tender cookie texture and a smooth, creamy buttercream.
- Kosher Salt: Salt balances the sweetness and helps the bright key lime flavor stand out.
- Key Limes: Fresh key limes bring bright, citrusy flavor to both the cookies and the marshmallow buttercream. The zest adds concentrated lime flavor without extra liquid, while the juice gives the cookies and filling their fresh, tangy taste. If you cannot find key limes, regular limes can be used instead.
- Vanilla Extract: Vanilla adds a warm flavor that balances the citrus and sweetness in both the cookies and the filling.
- All-Purpose Flour: All-purpose flour gives the cookies structure while keeping them soft and buttery.
- Marshmallow Creme: Marshmallow creme (also called marshmallow fluff) gives the filling its light, fluffy texture and sweet marshmallow flavor. You can use store-bought marshmallow creme or make my Homemade Marshmallow Fluff.
- Cream Cheese: Cream cheese adds a little tang to the marshmallow buttercream, balancing the sweetness and helping create a smooth, stable filling. Make sure it is softened before mixing.
Tips for the Best Key Lime Sandwich Cookies
- Use room temperature butter. Softened butter blends smoothly with the confectioners’ sugar and helps create a tender, buttery cookie.
- Measure the flour carefully. Too much flour can make these cookies dry or crumbly. For the best results, lightly spoon the flour into your measuring cup and level it off, or use a kitchen scale.
- Do not overmix the dough. Once the flour is added, mix just until a soft dough forms. Overmixing can make the cookies less tender.
- Flatten the cookies evenly. Since these cookies are sandwiched together, keeping them similar in size and thickness helps them bake evenly and makes assembly easier.
- Let the cookies cool completely before filling. Warm cookies can soften the buttercream and make it harder to assemble the sandwiches.
- Pipe the filling for the prettiest cookies. A piping bag makes it easy to add an even layer of Key Lime Marshmallow Buttercream, but you can also spread it with a small spatula or knife.
- Chill the assembled cookies if needed. A short chill helps the filling firm up and makes the sandwich cookies easier to handle.
FAQs
Can I make Key Lime Sandwich Cookies ahead of time?
Yes! These cookies are a great make-ahead dessert. You can bake the cookies a day or two in advance and store them in an airtight container until you are ready to fill and assemble them. The Key Lime Marshmallow Buttercream can also be made ahead and stored separately until ready to use.
Can I use regular limes instead of key limes?
Yes! Regular limes are a great substitute if key limes are not available. The flavor will be slightly different, but they will still give these cookies a bright, fresh citrus flavor.
How do I keep the filling from squishing out of the cookies?
For the cleanest sandwich cookies, make sure the cookies are completely cool before adding the filling. Pipe or spread the buttercream onto the flat side of one cookie, then gently press another cookie on top. If the filling feels too soft, chill the assembled cookies for 20 to 30 minutes before serving.
Can I make the cookies without the marshmallow buttercream filling?
Yes! The Key Lime Cookies are delicious on their own, too. They are buttery, tender, and full of fresh key lime flavor. The marshmallow buttercream adds a creamy, sweet filling that makes them extra special as sandwich cookies. You can also switch it up with another frosting or filling if you prefer. A simple vanilla buttercream or cream cheese frosting would also be delicious.
How to Store Key Lime Sandwich Cookies
Because the filling contains cream cheese, store assembled Key Lime Sandwich Cookies in an airtight container in the refrigerator. They will keep well for up to 5 days.
For the best texture and flavor, let the cookies sit at room temperature for a few minutes before serving. This allows the buttercream filling to soften slightly and makes each bite extra creamy.
If you prefer a softer cookie, you can let them sit out a little longer before enjoying them.
Can I Freeze Key Lime Sandwich Cookies?
Yes! Key Lime Sandwich Cookies freeze well, making them a great dessert to prepare ahead of time. Place the assembled cookies in a freezer-safe container, separating layers with parchment paper to prevent sticking. Freeze for up to 2 months.
When ready to enjoy, thaw the cookies in the refrigerator overnight or let them sit at room temperature until softened. For the best texture, allow them to come close to room temperature before serving.
Key Lime Sandwich Cookies
Ingredients
Cookies
- 1 cup (2 sticks / 227 g) unsalted butter, softened
- ¾ cup (90 g) confectioners' sugar
- ½ teaspoon kosher salt
- 1 tablespoon fresh key lime zest
- 2 tablespoons key lime juice
- ½ teaspoon vanilla extract
- 2 ¼ cups (280 g) all-purpose flour
Key Lime Marshmallow Buttercream
- ¼ cup (½ stick / 57 g) unsalted butter, room temperature
- ½ jar (3 ½ ounces) marshmallow creme (marshmallow fluff)
- 2 ounces cream cheese, room temperature
- 2 cups confectioners’ sugar
- ½ to 1 tablespoon key lime juice
- ½ teaspoon key lime zest
- 1 pinch kosher salt
- ¼ teaspoon vanilla extract
Instructions
Cookies
- Preheat oven to 375°F. Line baking sheets with parchment paper.
- In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, confectioners’ sugar, salt, and key lime zest until smooth and creamy.
- Add the key lime juice and vanilla extract and mix until combined.
- Gradually add the flour and mix just until a soft dough forms.
- Scoop the dough into 1-tablespoon portions. Roll each portion into a ball, then flatten to about ¼-inch thick using the bottom of a glass.
- Bake for 9 to 12 minutes, or until the cookies are set and the edges begin to turn golden. Let the cookies cool completely before filling.
Key Lime Marshmallow Buttercream
- 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.
- With the mixer on low speed, gradually add the confectioners’ sugar, mixing until smooth.
- Add ½ tablespoon of key lime juice, key lime zest, salt, and vanilla extract. Mix until combined.
- Taste and add more key lime juice, if desired, until the frosting 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 light and fluffy.
Assemble Cookies
- Pipe or spread about 1 to 2 tablespoons of Key Lime Marshmallow Buttercream onto the flat side of one cookie.
- Top with another cookie and gently press together.
- Repeat with the remaining cookies. For cleaner edges and a firmer filling, chill the assembled sandwich cookies for 20 to 30 minutes before serving.
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