1. Preheat Oven and Prepare Muffin Tins:

Preheat the oven to 350°F (175°C).

Line 24 muffin cups with paper liners.

2. Make the Key Lime Curd:

Combine the granulated sugar, key lime juice, egg, and egg yolk in a small saucepan over medium-low heat.

Whisk until the sugar dissolves, about 1 minute.

Whisking constantly, add the chilled, cubed butter, a few pieces at a time. Waiting until each addition melts before adding more.

Continue whisking until the curd is thick and coats the back of a spoon, 3 to 4 minutes.

Transfer the curd to a small bowl and refrigerate until chilled, about 1 hour.

3. Make the Cupcakes:

While the curd is chilling, make the cupcakes.

Prepare the white cake mix according to the package directions for cupcakes. This usually involves combining the mix with eggs, oil, and water.

4. Bake the Cupcakes: Bake the cupcakes as directed on the cake mix box. Usually around 18-22 minutes.

Or until a wooden pick inserted in the center comes out clean.

5. Cool the Cupcakes:

Allow the cupcakes to cool in the muffin tins for a few minutes.

Then remove them to a wire rack to cool completely.

6. Make the Frosting:

While the cupcakes are cooling, make the frosting.

Beat the softened butter, softened cream cheese, and key lime juice in a large bowl with a mixer on medium-high speed until light and fluffy, 3 to 4 minutes.

Reduce the speed to low and slowly add the powdered sugar.

Continue to beat until just combined, 1 to 2 minutes.

7. Fill and Frost the Cupcakes:

Once the cupcakes are completely cool, use a paring knife to cut a small hole in the top of each cupcake, about ½ inch deep and ½ inch in diameter.

Spoon ½ teaspoon of the chilled key lime curd into each hole.

Spread or pipe the key lime cream cheese frosting on top of the cupcakes.

8. Garnish and Serve:

Sprinkle the frosted cupcakes with graham cracker crumbs.

Top each cupcake with a thin lime slice.

Serve and enjoy your delicious Key Lime Pie Cupcakes!