In the top of a double boiler whisk together key lime juice, sugar and eggs until combined. Cut butter into 4 pieces and add to mixture. Place the mixture over simmering water. Stir constantly until the mixture thickens and coats the back of a spoon. (160 degrees on a thermometer) Strain through a fine strainer into a bowl. Cool slightly, then place in refrigerator with a piece of plastic wrap against the surface. The curd will keep for one week in the refrigerator.
Preheat oven to 375 degrees. Line a 9x9 square pan with parchment paper, extending the parchment over the edges. Spray the parchment lightly with non-stick cooking spray.
In a large bowl beat the butter by hand with a rubber spatula for 1-2 minutes. Add the granulated sugar and vanilla and continue to beat until combined, scraping down the bowl occasionally. In a small bowl whisk together flour, salt and baking powder. Add flour mixture to butter mixture until well combined. The mixture will be somewhat crumbly. Press mixture into the bottom of the prepared pan reserving about 2/3 cup for the crumb topping.
Bake crust for 12-14 minutes until golden brown. Remove from oven and top with key lime curd spreading to within 1/2 inch from outer edge. Add the almonds and coconut to the reserved crumb topping. Toss lightly with your fingers. Sprinkle mixture over the key lime curd.
Bake for 22-24 minutes until golden brown. Cool in the pan on a wire rack. Lift bars out of pan by the parchment overhangs. Cut into bars.