Preheat oven to 180ºC. Grease 2 x 23cm round cake pans with butter; sprinkle lightly with flour.
Beat cake mix, oil, water and eggs in a large bowl with electric mixer on low speed until moistened. Beat on medium speed for 2 minutes. Fold in the 50g of coconut.
Divide the mixture evenly between the cake pans. Bake 25 to 30 minutes until golden and toothpick inserted in center comes out clean. Cool 10 minutes. Run knife around sides of pans to loosen cakes; remove from pans to cooling rack. Cool completely.
Beat whipping cream mix and cold milk in medium bowl as directed on package.
Place one cake on a serving plate. Top with lemon curd; spread evenly. Top with the second cake and press down gently.
Spread a thin layer of whipping cream over top and sides of cake to seal in crumbs. Spread remaining whipping cream in a thicker layer over entire cake. Sprinkle the toasted coconut over top of the cake.