In small bowl combine butter and granulated sugar until crumbly. Set aside.
Bread Batter
Preheat oven to 350°F and grease two 4 1/2-inch by 8 1/2-inch loaf pans and line bottom with wax paper.
In medium bowl mix salt, baking soda, and flour. Set aside. In large bowl combine brown sugar, vanilla, and oil. Mix until smooth. Stir in egg and buttermilk.
Add dry ingredients to wet and blend until all dry ingredients are incorporated with wet but do not over-mix.
Fold in rhubarb and nuts. Turn batter into two greased 4 1/2-inch by 8 1/2-inch loaf pans. Sprinkle streusel topping over batter dividing evenly between two pans.
Bake at 350°F for 50 to 55 minutes or until cake tester inserted in the middle comes out clean. Turn out onto racks and remove wax paper before slicing. Makes 8 to 10 slices per loaf. Enjoy!