These Key Lime Cupcakes are the kind of dessert that instantly makes everything feel a little brighter. The cupcakes are soft and buttery with plenty of fresh key lime flavor, and the key lime ermine frosting is light, silky, and perfectly tangy without being overly sweet. They’re great for spring and summer gatherings, birthdays, baby showers, or honestly just when you’re craving something fresh and citrusy. If you love key lime desserts as much as I do, make sure to try my Key Lime Pie Bars and Easy No-Bake Key Lime Pie, too. Both are great options when you want that sweet-tart key lime flavor in an easy make-ahead dessert.
Ingredients & Substitutions
- All-purpose flour: Gives the cupcakes a soft, tender crumb. You’ll use flour in both the cupcakes and the ermine frosting, so measure carefully for the best texture.
- Baking powder: Helps the cupcakes rise with a light, fluffy texture.
- Kosher salt: Balances the sweetness and brightens the citrus flavor.
- Unsalted butter: Adds richness to both the cupcakes and frosting. Let it fully come to room temperature before mixing. If using salted butter, you may want to lessen the amount of salt.
- Granulated sugar: Sweetens the cupcakes and frosting without overpowering the fresh lime flavor.
- Eggs: Help create structure while keeping the cupcakes soft and tender.
- Whole milk: Adds moisture and richness. You can substitute buttermilk for an even softer crumb and a slightly tangy flavor.
- Key lime juice and zest: You’ll use fresh key lime juice and zest in both the cupcakes and the frosting, so plan on several key limes. Fresh juice gives the brightest flavor, while the zest adds even more citrus aroma and color. Regular limes can work if needed, but key limes have a more tart, floral flavor.
- Key Lime Ermine frosting: Instead of a traditional buttercream, these cupcakes are topped with a cooked ermine frosting made with key lime juice, flour, butter, sugar, key lime zest, vanilla, and salt. It’s silky, light, and creamy with a less-sweet finish that lets the citrus flavor shine.
FAQs
Can I use regular limes instead of key limes?
Yes, regular limes will work if that’s what you have on hand. The flavor will be slightly less floral and more tart, but still delicious. If possible, try to use fresh juice and zest for the brightest citrus flavor.
Why is my ermine frosting too soft?
Ermine frosting can soften if the cooked flour mixture isn’t fully cooled or if the butter is too warm. If this happens, pop the frosting in the refrigerator for 15 to 30 minutes, then re-whip it until light and fluffy again.
Can I make key lime cupcakes ahead of time?
Yes. You can bake the cupcakes a day in advance and store them in an airtight container at room temperature. Frost them just before serving for the best texture and appearance.
Do I have to use ermine frosting?
No, but it really makes these cupcakes special. You can also use a classic buttercream or whipped cream cheese frosting if preferred, though ermine keeps things lighter and lets the lime flavor shine.
How do I get the strongest key lime flavor?
Use both fresh zest and juice, and don’t skip the zest; it carries a lot of the essential citrus oils. Feel free to use up to 4 tablespoons in the cupcake. You can also add a little extra zest to the frosting if you want a stronger lime punch.
How to Store Key Lime Cupcakes with Key Lime Ermine Frosting
Room Temperature: Because these cupcakes are topped with ermine frosting, they can be stored at room temperature for up to 1 to 2 days. Keep them in an airtight container in a cool spot away from direct sunlight. Ermine frosting holds well, but it’s soft, so try not to stack the cupcakes.
Refrigerator: For longer storage, refrigerate the cupcakes for up to 4 to 5 days. Place them in an airtight container so they don’t absorb fridge odors. Before serving, let them sit at room temperature for about 20 to 30 minutes so the frosting softens and the texture becomes light and creamy again.
Freezer: These cupcakes also freeze well. Freeze unfrosted cupcakes for best results, or freeze fully frosted cupcakes on a tray until solid, then transfer to an airtight container. Freeze for up to 2 months. Thaw overnight in the refrigerator and bring to room temperature before serving.
Key Lime Cupcakes with Key Lime Ermine Frosting
Ingredients
Key Lime Cupcakes
- 1 ½ cups (187.5 g) all-purpose flour
- 1 ½ teaspoons baking powder
- ½ teaspoon kosher salt
- ½ cup (1 stick / 113 g) unsalted butter, softened
- ¾ cup (150 g) granulated sugar
- 2 large eggs, room temperature
- ½ cup whole milk, room temperature
- 1 teaspoon vanilla extract
- 1* tablespoon key lime zest, from 1 to 2 key limes
- ⅓ cup key lime juice, from about 8 to 12 key limes (or bottled key lime juice)
Key Lime Ermine Frosting
- ¾ cup fresh key lime juice, from about 18 to 24 key limes (or bottled key lime juice)
- 5 tablespoons all-purpose flour
- 1 cup (2 sticks / 227 g) unsalted butter, room temperature
- 1 cup (200 g) granulated sugar
- 2 to 3 tablespoons key lime zest, from 3 to 4 key limes
- ½ teaspoon vanilla extract
- Pinch kosher salt
Instructions
Key Lime Cupcakes
- Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
- In a medium bowl, whisk together the flour, baking powder, and salt.
- In the bowl of a stand mixer with the paddle attachment (or using a handheld mixer), beat the butter and sugar until light and fluffy, about 2 to 3 minutes.
- Add the eggs one at a time, beating well after each addition.
- Mix in the vanilla extract, key lime zest, and key lime juice.
- With the mixer on low speed, add half of the flour mixture. Pour in the milk and mix until combined. Add the remaining flour mixture and mix just until incorporated. Do not overmix.
- Divide the batter evenly among the cupcake liners, filling each a little over halfway full.
- Bake for 20 to 24 minutes, or until the tops spring back lightly when touched and a toothpick inserted into the center comes out clean.
- Let the cupcakes cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
Key Lime Ermine Frosting
- In a medium saucepan over medium heat, whisk together the key lime juice and flour until smooth.
- Cook, whisking constantly, until the mixture thickens to a pudding-like consistency and begins to bubble, about 2 to 4 minutes. Continue cooking for 1 additional minute while whisking.
- Remove from heat and transfer the mixture to a shallow bowl or plate. Press plastic wrap directly onto the surface and let cool completely to room temperature.
- In the bowl of a stand mixer with the paddle attachment (or using a handheld mixer), cream the butter and sugar together on medium-high speed until very light and fluffy, about 4 to 5 minutes.
- Add the cooled lime mixture, lime zest, vanilla extract, and salt. Beat on medium speed until combined, then increase to high speed and whip until smooth, light, and fluffy, about 3 to 5 minutes more.
- If the frosting feels too soft for piping, refrigerate for 15 to 30 minutes before frosting the cupcakes.
- Pipe or spread frosting onto completely cooled cupcakes and garnish with additional lime zest if desired.
Notes
Did you make this recipe?
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