The cake can be kept at room temperature in an airtight container for up to 3 days. The layers can be frozen separately for 1 month.
To grate fresh coconut, crack open a whole coconut; discard the liquid. Place the coconut pieces on a baking sheet and bake at 350° for 5 minutes to loosen the flesh from the shell; let cool. Peel the brown skin from the coconut meat, then shred the pieces in a food processor using the fine grating disk.
Be sure the cakes are completely cool before cutting them into layers. To help reassemble the cake halves evenly after cutting and spreading them with jam, place two toothpicks on top of each other on the side of the cakes, one near the top and the other near the bottom. Slice the cakes in half between the toothpicks and spread the bottom layers with jam as directed by the recipe. To reassemble, simply replace the top layers, lining up the toothpicks.
Sparkling wine is an elegant partner for this classic cake. Avoid a dry brut, which will taste metallic. Instead, opt for a sweeter, rounder-textured bottling, such as a demi-sec.