In a small bowl of lukewarm water, soak rosemary leaves and raisins. Set aside.
Make sure your oven rack is in the center position. Preheat oven to 350°F. Grease a 9” pie pan with olive oil or a non-stick cooking spray, then set aside.
Combine chestnut flour, water, honey, and olive oil in a large bowl using a fork. Continue stirring with fork until a smooth batter forms. If the batter is too thick, you can add a tablespoon or two of water to thin the batter slightly.
Drain rosemary leaves and raisins, then pat dry. Add half of the raisins, walnuts, and pine nuts to the batter. Stir to combine all ingredients.
Into the prepared pie pan, pour batter. Using a spatula, spread the batter so it forms a smooth and uniform layer. Evenly distribute the rosemary as well as the remaining raisins, pine nuts, and walnuts on top of the batter.
Place the pie pan into a pre-heated oven. Bake for 30-35 minutes, or until the top of the cake is dried and starting to crack.
Remove the cake from the oven and allow it to cool slightly before cutting. Slice it into thin slices and serve.
*Honey is optional. Use more or less honey depending on your desired level of sweetness.