Preheat the oven to 190 C (375 F). In a bowl, mix together one and a half ounces of butter and sugar on a medium to low speed until it is light and fluffy for about 4 minutes. Add some vanilla seeds and sour cream and mix together for about 2 minutes. Add your eggs one at a time. Then, add baking soda, flour, salt and then mix together until all is combined.
Pour the mixed batter in a loaf pan and sweep around in a even motion with a rubber spatula. Bake till you can use a toothpick to check if it comes out clean. Bake for 50 minutes to an hour. Move the pan to the wired rack and let the cake cool for 30 minutes and invert the pan to let the cake release. Let it cool completely on a rack for 2 hours.
In a regular sized saucepan, put on medium to high heat. Bring the ginger, 2 tablespoons of water, rhubarb and the leftover sugar to boil. Put the heat to simmer and cook until the rhubarb has gone down to chunks for 8 to 10 minutes. Remove the saucepan from the heat and let the rhubarb to cool for at least 2 hours. To serve, cut the cake into 8 even pieces. Put some whipped cream on each slice.