Heat oven to 350º.
In a large bowl, mix 1 cup granulated sugar, brown sugar, butter, egg, buttermilk, baking soda, vanilla, flour, and rhubarb, one at a time in the order given.
In a separate bowl, combine ¼ cup granulated sugar, cinnamon, and nuts.
Stir half of nut mix into cake batter. Pour cake batter into large loaf pan. Sprinkle reserved nut mix on top.
Bake 30-40 minutes.