Preheat the oven to 175C / 347F and prepare your tart tins by spraying with cooking spray and lining the base with baking paper.
In a food processor, combine the almond flour and macadamia nuts and process on high speed until the nuts have become a flour (it's ok if it's a little chunky!)
Add the butter, xylitol and egg yolk to the nut flours and process until it has combined completely.
Press the crumb mixture firmly into the base of the tart tin. This is easiest using your hands.
Bake in the oven for 12 - 15 minutes until lightly golden.
Lime Cheesecake Filling
Prepare the limes by zesting and juicing both completely. Set 1 teaspoon of zest aside for serving.
In the food processor, add all filling ingredients including remaining lime zest (reserving 1 teaspoon for serving) and lime juice. Process on high until combined evenly.
Assembly
One the crusts are cooked, pour in the filling mixture and spread evenly.
Return to the oven for 18 - 20 minutes until lightly golden.
Refrigerate until ready to serve. When ready, whip the cream and pipe or spread on top of the pie and sprinkle with remaining lime zest.