Preheat your oven to 350°F (175°C). This ensures that your cupcakes bake evenly and rise properly.

Line a cupcake tin with cupcake liners. This prevents the cupcakes from sticking and makes for easy removal.

In a mixing bowl, cream together the softened butter and granulated sugar using an electric mixer on medium speed until light and fluffy, about 3-4 minutes. This incorporates air into the mixture, helping the cupcakes to rise.

Add the eggs one at a time, mixing well after each addition. This helps to emulsify the mixture, creating a uniform batter.

In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. This ensures even distribution of the leavening agents.

In another bowl, combine the buttermilk, lime juice, and tequila (if using).

Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk mixture, starting and ending with the dry ingredients. Mix until just combined; do not overmix to keep the cupcakes light and fluffy.

Spoon the batter into the prepared cupcake liners, filling each about ⅔ full. This allows room for the cupcakes to rise.

Bake in the preheated oven for 15-18 minutes, or until a toothpick inserted into the center comes out clean. This indicates that the cupcakes are fully baked.

Remove from the oven and let the cupcakes cool in the tin for 5 minutes before transferring them to a cooling rack to cool completely.

In a mixing bowl, beat the softened butter on medium speed until creamy, about 1-2 minutes. This helps to create a smooth base for the frosting.

Gradually add the sifted powdered sugar, mixing on low speed until combined. This prevents the sugar from flying out of the bowl.

Add the lime juice, lime zest, and vanilla extract. Beat on medium speed until the frosting is light and fluffy, about 3-4 minutes. This incorporates air into the frosting, making it light.

Once the cupcakes are completely cooled, use a piping bag fitted with a star tip to frost each cupcake generously with the lime buttercream.

Garnish each cupcake with a slice of lime and rim the edges with coarse sea salt for an authentic margarita touch.