Lime-vanilla Buttercream

To a small bowl, add lime juice, lime zest and vanilla, whisk together and set aside.

Place egg whites and sugar in the bowl of a stand mixer and whisk to blend. Bring 2 inches of water to a simmer in a medium saucepan. Place the bowl over the simmering water and heat, whisking constantly, until the mixture reaches 145° F on an instant-read thermometer. Remove bowl from the heat and attach to a stand mixer fitted with a whisk attachment. Whip the mixture on high speed until it cools to room temperature, is light and billowing, and resembles marshmallow fluff. Before continuing, make sure the meringue is cooled to room temperature; otherwise the butter added in the next step will melt.

With the mixer on medium-high speed, add the butter a couple of tablespoons at a time, allowing each addition to blend in fully before adding the next. Halfway through adding the butter, stop the mixer and use a silicone spatula to scrape down the sides of the bowl thoroughly. Continue to whip until all the butter has been added and the mixture is velvety and smooth. Add the lime-vanilla mixture; whip to incorporate. Buttercream may appear to break, continue to whip until smooth and creamy. Transfer lime-vanilla buttercream to a piping bag fitted with a medium plain round pastry tip.

Fill and assemble macarons.