Preheat oven to 375 degrees Fahrenheit (or 400˚F for high altitude). Line cupcake pans with paper liners.

In a medium bowl, whisk together the flour, baking powder, and salt; set aside.

In a large bowl, whisk together the oil and sugar. Add eggs one at a time, whisking well after each addition. Add the lime juice and zest and mix until combined.

Add the flour in three additions, alternating with the buttermilk in two additions, beginning and ending with the flour. Scrape the bowl as necessary. Mix until just combined. Do not over-mix. Fill each cupcake liner ⅔ full (not ¾ or they will overflow).

Bake at 375˚F (or 400˚F for high altitude) for 15-20 minutes or until cake springs back when touched or a toothpick inserted into the middle comes out with just a few moist crumbs. Cool completely before frosting.

FOR THE FROSTING: Using a hand mixer, beat cream cheese until smooth. Gradually add the butter 2 Tablespoons at a time, and continue beating until smooth and well blended. Add key lime juice and lime zest. Mix and scrape bowl. Add powdered sugar all at once and mix until just combined. CHILL frosting for 30 minutes before piping on top, if frosting seems too soft. Frost cupcakes as desired. (*If piping high, 1.5x the recipe.)