For cookies: Preheat oven to 400˚F.
In a mixing bowl, combine flour, baking powder and lime zest. Whisk together and set aside.
In a stand mixer, fitted with a paddle attachment (or with a hand mixer), cream together butter and sugar. Until light and fluffy.
Add egg and vanilla to the butter mixture and continue to mix together.
Stir the dry mixture into the wet mixture and beat together until smooth dough forms, scraping down the sides of the bowl as needed.
Lightly dust a clan surface and roll the dough out until about ¼” thick.
Using your pineapple cookie cutter, cut out as many cookies as possible, rerolling the dough scraps as needed.
Transfer cookies onto a parchment lined baking sheet, about 1 ½” apart and bake for 7-9 minutes or until the cookies have just baked through and are barely brown around the edges.
Allow cookies to cool completely before frosting.
Pineapple buttercream: In a mixing bowl beat butter until light and fluffy. Add sugar, 1 cup at a time, until fully incorporated (the mixture will be extra stiff and thick at this point). Beat in pineapple juice, 1-2 tablespoons at a time until fully incorporated and the buttercream is light and fluffy.
To assemble: Divide the buttercream into 2 mixing bowls. The first bowl should have ¾ of the buttercream mixture with the remaining buttercream in the second bowl. Add a couple drops of yellow food coloring into the first batch and a couple drops of green into the second (if using professional grade, you’ll only need a drop or two the size of a pinhead) and mix together until smooth and each buttercream batch is uniformly one color.
Fill a piping bag, fitted with a small star tip, with the yellow buttercream. Pipe small beads of buttercream, at a 45˚angle, in straight rows, over the rounded base of the cookie.
Once all the bodies of the cookies have been frosted, fill another piping bag, fitted with a small circle tip, with the green colored buttercream.
Pipe the green buttercream over the leafy tops of the pineapple cookies to finish decorating.
Set cookies aside and allow buttercream to slightly hardened. Serve.