The night before the cake is to be baked, combine the raisins and sherry, cover and soak overnight.
Place the oven rack in the middle position and preheat oven to 350 degrees F. Butter two 9 inch cake pans and dust with flour.
In a medium bowl, sift the flour, baking soda, and salt together; set aside.
Place the butter and sugars in the bowl of a stand mixer; mix until uniformly creamy. Add the eggs, one at a time, beating to combine after each addition. Stir in the vanilla and orange zest.
Alternate adding the flour and buttermilk a portion at a time and beating well after each addition. Stir in the pecans and raisins with sherry until just completely incorporated.
Distribute the batter equally into the prepared pans. Bake 35 - 40 minutes, rotating the pans half way. The cake should be golden, begin to pull away from the edge of the pan, and springs back when lightly touched in the center.
Cool 10 minutes before inverting onto wire racks. Cool completely before frosting.