Preheat oven to 350 degrees F. Lightly grease two 8 inch cake pans and line the bottoms with parchment paper.
Combine the cake mix, coconut milk, egg whites and oil in the bowl of your stand mixer and beat on low for 30 seconds, then medium for 2 minutes. Add the coconut extract and 1/2 cup of shredded coconut to the batter, stir to combine. Divide mixture between the two pans (batter will be thick), and spread evenly. Bake for 30 to 33 minutes, or until cake springs bake when gently pushed. Let cool for 15 minutes in pan before placing on wire rack to cool completely.
Meanwhile spread the remaining 1 cup of shredded coconut on a parchment lined baking sheet and bake at 350 degrees for 6 to 7 minutes, stirring halfway through. Remove from oven and let cool.
Once cake is cool cut each layer in half (I froze my layers to make them easier to cut). Spread 1/3 of the lemon curd on each layer, then top with the last layer of cake.
To make the Frosting:
Combine the butter and pinch of salt in the bowl of your stand mixer fitted with the paddle attachment and beat until light and fluffy. Add the coconut extract and powdered sugar, then start the mixer on low speed until the butter mixture absorbs the sugar. Add two tbsp of coconut milk and turn the speed up to medium/high and beat for 2 to 3 minutes. If the frosting needs to be thinner, add more coconut milk and continue beating until combined.
Frost the layered cake and then top with the toasted coconut and optional toppings if desired.
If you prefer, you could skip cutting each layer in half and simply have two layers rather than four. Just reduce the amount of lemon curd by half.