Preheat the oven to 350° Fahrenheit.
In a stand mixer with the paddle attachment, add the oil (preferrably butter) and brown sugar. Mix until well combined.
To the bowl add the room temperature sour cream. Mix again until smooth. Add in the vanilla.
Now add in one egg at a time mixing after each egg is added. I think you get the picture of adding in one ingredient at a time and mixing!
To the mixture add in the salt and baking soda. Mix that together.
To the creamed mixture, add in half of the einkorn flour, mix well, then add in the other half. Make sure all lumps are blended out.
Remove the bowl from the stand mixture and stir in the chopped rhubarb.
In a well greased 9 inch round cake pan or a parchment lined pan, pour in the cake batter.
Bake in the 350 degree preheated oven for 40 minutes or until golden brown on top and/or toothpick inserted in the middle comes out clean.
Let cool for 10 minutes. At this time use a butter knife to separate the cake from the edge of the pan to make it easier to flip out. If you prefer, you can just leave the cake in the pan, but I like the presentation of it out of the cake pan.
Flip the cake out onto a serving platter and let cool completely before frosting if you so desire. Frost the cake with the simple maple cream cheese frosting or enjoy it plain.
This cake is also delicious with a little rhubarb jam on top or fresh strawberries.