Preheat the oven to 350F. Thoroughly coat the inside of a 12-cup Bundt pan with baking spray, set aside.
In a bowl, combine the flour, salt and baking soda. Set aside.
Combine the eggs and brown sugar in a mixer for 2 minutes.
Add the butter and vanilla. Mix for another 3 minutes.
Add in the buttermilk and combine.
Add the flour mixture gradually and beat briefly until smooth. Set aside
In a small bowl, combine the filling ingredients and set aside.
Pour about one half of the batter into the prepared pan (you can do this by eye). Smooth it with a small offset spatula. Sprinkle with filling and top with remaining cake batter, smoothing the top.
Bake the cake for about 1 hour or until a toothpick inserted in the center of the cake portion shows a few moist crumbs when removed. Let cool for about 30 minutes, then unmold onto rack and cool completely.
