* I like to chop up rhubarb and add it to a medium pot, with about 1/2 cup water. Heat to low and cook rhubarb til it is completely soft. Take off heat and you can the use this softened rhubarb in muffins or other baking.
Lightly grease a 9×13 pan with butter.
Line the bottom with parchment paper.
Heat oven to 350 degrees.
In stand mixer, beat butter with brown sugar until light and fluffy.
Beat in eggs, one at a time, then add vanilla.
In a small bowl, whisk the flour, baking soda, baking powder and salt.
Slowly add dry ingredients to butter mixture, while alternating with the buttermilk.
Beat until cake batter is smooth.
Fold in rhubarb and pour into cake pan.
Bake for 35-45 minutes until cake is done.
Serve warm or cold.