Blackberry Jam Cake

2 cups blackberry jam, room temperature
1 cup butter, salted, softened
1 cup black walnuts, chopped
2 cups butter, salted, softened
6 eggs, room temperature
2 tsp. nutmeg, ground
1 cup raisins
2 tsp. cinnamon, ground
2 tsp. baking soda
4 cups flour
1/2 tsp. salt
2 cups buttermilk, room temperature

Preheat the oven to 350° F (176°C). Butter and flower a large tube pan, or use a flour-based baking spray such as Baker's Joy. Set the pan aside.
Separate the eggs, putting the yolks and whites in different mixing bowls. I another large bowl, mix together the flour, baking soda, salt, cinnamon, and nutmeg. In a small bowl, mix ½ cup of the flour mixture with the black walnuts and raisins.
Add the brown sugar, butter, and blackberry jam to the egg yolks, and stir together thoroughly. Stir in the buttermilk. Add the flour mixture.
Beat the egg whites until they turn white but are loose and runny, not too "airy." Fold the egg whites into the batter. Then mix the nuts and raisins, blending only enough so that they are equally distributed in the batter.
Pour the batter into the tube pan and bake for 1 ½ to 2 hours. When a toothpick inserted in the center comes out clean, it's done.
Remove the pan from the oven and let the cake cool for about 10 minutes in the pan. Then loosen the cake from the sides of the pan by running a knife around the edge. Invert a cake plate over the pan, and invert the tow together. Lift off the tube pan.
Slice and serve.