1. Preheat the oven to 325 degrees.
2. To make the cake: In a large bowl, mix together the flour, kudzu, cream of tartar, mint, baking soda, salt, nutmeg, and cardamom.
3. In a small bowl, mix together the apple juice, almond oil, vinegar, and vanilla. Mix the wet ingredients into the dry ingredients, being careful not to overmix. Mix in the berries, drained raisins, and walnuts.
4. Pour the batter evenly into 2 oiled 9-inch round cake pans. Bake the cakes until a toothpick inserted in the center emerges clean, about 30 minutes. Let the cakes cool on a wire rack.
5. To make the filling: Simmer all the filling ingredients except the berries together in a medium-size saucepan over low heat for 10 minutes, stirring occasionally. Stir in the berries, remove the pot from the heat, and let the filling stand for 5 minutes.
6. Test the firmness of the filling by half-filling a metal spoon with the filling and placing it in the freezer for a few minutes, until the filling is chilled. The filling should be as firm as jam. If not, add more agar and simmer the filling for another 10 minutes, or thin the filling by adding more apple juice. Test the filling until the consistency is right.
7. When the cake layers are cool, spread half the filling on one cake, place the other cake on top, and spread the remaining filling on top.