In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In a separate large bowl, beat the butter and sugar together until light and fluffy, about 2-3 minutes.
Add the eggs, one at a time, beating well after each addition.
Add the lilikoi juice, buttermilk, and vanilla extract to the butter mixture, and beat until well combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Divide the batter evenly between the two prepared cake pans.
Bake the cakes for 25-30 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
Allow the cakes to cool in the pans for 5 minutes, then remove them from the pans and let them cool completely on a wire rack.
While the cakes are cooling, make the lilikoi curd. In a medium saucepan, whisk together the lilikoi juice, sugar, and egg yolks.
Cook the mixture over low heat, stirring constantly, until it thickens enough to coat the back of a spoon.
Remove the saucepan from the heat and stir in the butter until it is melted and well combined.
Strain the curd through a fine mesh sieve to remove any lumps or solids, then cover it and refrigerate until it's chilled and set, about 1 hour.
Once the cakes and curd are completely cooled, it's time to assemble the cake. Place one cake layer on a serving plate or cake stand.
Spread a thick layer of lilikoi curd over the top of the cake layer, making sure to spread it evenly.
Place the second cake layer on top of the curd layer, pressing down gently.
To make the whipped cream frosting, whip the heavy cream, powdered sugar, and vanilla extract together in a large bowl with an electric mixer until stiff peaks form.
Spread a generous layer of whipped cream frosting over the top and sides of the cake.
Decorate the cake with fresh lilikoi fruit or any other tropical fruit of your choice.
Serve and enjoy your delicious homemade lilikoi cake!