1. Place 3 Grass, 2 Branches, 2 Flint, 2 Dried Fruit, and 1 Ice into a book of techs, and click on the unlock icon in the center-left to unlock all of the techs.
2. Once you have unlocked all the techs, unlock the recipe for the Eternal Fruit Cake, which requires 1 salvia and 4 different types of jam.
3. The Sagebrush Paper requires 4 Grasses and 1 Twig, which can be obtained by transplanting turf or by scavenging.
4. Jam requires different types of fruits, which can be grown or scavenged.
5. To make the Eternal Fruit Cake, you need to collect all the Sarcophagi and 4 different kinds of jam.
6. Put all the salvia and jams into a tech book and click the unlock icon in the center to unlock the Eternal Fruit Cake.
The above are all the steps to make Famine Eternal Fruit Cake for your reference.