Key Lime Curd 

1. Whisk sugar, key lime juice and eggs in saucepan over low heat until sugar dissolves.
2. Add butter and continue whisking until curd thickens and begins just to bubble; cook 1 more minute.
3. Remove from heat and strain through a fine mesh to remove any bits of over cooked egg.
4. Cover and chill. Makes 3 cups.
5. For the Lime Scented Cake: Heat oven 350F. Spray three 9-inch cake pans with no-stick baking spray. Line bottom of pans with parchment paper circles. Spray parchment with baking spray.
6. In bowl, whisk both flours, baking powder and salt; set aside.
7. In stand mixer bowl, beat butter, sugar and zest until light and fluffy. Beat in eggs, 1 at a time, beating well after each addition. Add lime juice; blend well.
8. Fold in flour mixture by hand until fully incorporated.
9. Divide batter evenly among prepared pans.
10. Bake 18 to 20 minutes or until wooden pick inserted in center comes out clean. 
11. Turn out the cakes onto a wire rack, peel off the paper; cool completely. 
12. For the Lime Meringue Butter Cream:Place egg whites and sugar in the metal bowl of a stand mixer. Place the bowl over a pan of simmering water. Whisk the egg whites and sugar until the sugar dissolves and the mixture reaches 140F on an instant read thermometer.
13. Transfer bowl to stand mixer and using the whisk attachment at medium speed whisk mixture to stiff peaks. The bowl should now feel cool.
14. Switch whisk attachment to paddle attachment.
15. Reduce speed to a notch lower and start adding butter, 1 tablespoon at a time, making sure each tablespoon is well mixed before adding another. It may look curdled, but that is normal.
16. Now beat for 10 to 15 minutes until smooth.
17. Add lime juice and salt; beat well.
18. Place 1 cake layer on serving plate; top with 1/3 of the lime curd.
19. Place second cake layer on top and spread with half of the remaining lime curd.
20. Top with remaining cake layer and remaining curd leaving an edge of about ½-inch.
21. Place about ½ to 1 cup of butter cream into a piping bag with a star tip.
22. Spread remaining butter cream on sides of cake.
23. Pipe butter cream around top edge of cake and at bottom edge.
24. Dust cake rim and sides with finely crushed graham crackers.