Prepare a 1 lb or 1.25 lb loaf pan: grease with butter or line with parchment paper
Chop about 3 stalks of rhubarb, the total should be 2 cups. Set aside.
Using a stand mixer cream the butter and sugar together until smooth.
Add the eggs, one at a time, then the vanilla, and mix well.
In a separate bowl, whisk together the flour, baking powder, baking soda and salt.
Add the flour mixture, alternating with the buttermilk, to the butter mixture. Combine.
Stir in the chopped rhubarb.
Add the batter to the prepared pan, smoothing out the top.
Sprinkle the top with sugar if you want (you really should add it!).
Bake for about 1 hour and 10 minutes, until a toothpick inserted into the centre of the bread comes out clean. The top of the bread should also be golden brown.
Let cool for about 5 minutes in the pan, then remove and transfer to a wire rack to cool.