Key Lime Pie Macarons

• Preheat your oven to 300ºF and line three cookie sheets with parchment paper.
• Sift together the almond flour and powdered sugar, pressing through the sieve to break up all clumps.
• In a separate bowl beat the egg whites, cream of tartar and salt until frothy. Gradually add in the sugar and beat until just stiff and shiny.
• Add 1/3 of the egg white mixture into the almond mixture and whisk to combine. Fold in the rest of the egg whites into the almond mixture until no white streaks are left. Add in lime zest and food coloring, folding the mixture until it falls off the spatula in a ribbon, about 2-3 minutes.
• Transfer the mixture to a pastry bag fitted with a 1/4-inch round tip. Holding the pastry bag vertical and close (but not touching) the cookie sheet, pipe 1-inch circles. Tap the baking sheets on the counter once or twice to release air bubbles.
• Let the cookies sit until the tops are no longer sticky. Depending on the humidity this can take 30 minutes to an hour. Place one pan in the oven and bake until shiny and a foot forms, about 20 minutes. Remove from the oven and transfer to a cooling rack. Repeat with the remaining cookie sheets. Let cool completely.

For The Key Lime Filling

• In a bowl which can be used as a double boiler, whisk together the egg yolks, sugar, zest, key lime juice and salt. Place over a double boiler and cook over medium-low heat, whisking constantly until thickened, about 7 minutes.
• Remove the curd from the heat and whisk in the butter. Place in a bowl and cool to room temperature. Chill in the fridge for 1 hour until set.

To Assemble the Macarons

• Add a dollop of filling to the bottom of a macaron and top with graham cracker crumbs. Sandwich with another macaron and let set. Serve.