For the cake: Preheat the oven to 325 degrees F. Mix together the softened butter with 2 tablespoons of the flour to make a paste. In a 10-inch Bundt pan, paint on the flour and butter paste with a pastry brush until the pan is well coated.
Using an electric mixer, beat the sugar, oil and eggs until smooth. Add the orange juice and vanilla extract and mix well. In another bowl, sift together the baking soda, cinnamon, salt and remaining 3 cups flour. Add the flour mixture to the sugar mixture and continue to beat well. Stir in the apples and walnuts.
Pour the batter into the pan and bake until a toothpick inserted in the cake comes out clean, about 1 hour 30 minutes. Remove the cake from the oven and let it cool in the pan for 15 minutes. Turn the cake out onto a cake plate.
For the glaze: Combine the sugar, butter, buttermilk and baking soda in a large saucepan and bring to a boil. Boil the mixture until it thickens slightly and begins to turn a light brown, 5 to 10 minutes. Remove from the heat.
Using a toothpick, punch 15 to 20 holes in the top of the cake and pour the glaze over the cake. Let the cake set and cool before serving. Store the cake in an airtight cake carrier in the refrigerator for up to 2 weeks.