Cream butter and sugar together, then add in eggs and buttermilk and beat for 3 minutes.
In another bowl, mix the flour, baking soda and salt. Slowly add the dry mixture to the wet and mix together. The batter will be thick. You will spread it, rather than pour it. Spread a little more than half the mixture in the pan.
In another bowl, mix together the filling ingredients until well blended and then spread the filling layer over the cake batter. Add the rest of the batter on top of the filling.
In a small bowl, mix the topping ingredients together with a fork or your fingers until you get crumbs and sprinkle them over the top.
Bake for 45 minutes and then check. It should be golden brown and look set in the middle (not too jiggly.) Bake for additional 3-5 minute increments as needed.
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