For the Cake:
Warm the oven to 350F.
Beat the Eggs with the sour cream. Add the oil and vanilla and then add the dry ingredients. Leave a little flour to dust the berries with.
Batter will be thick. Bake in a tube pan for 40-45 mins.
For the Sauce:
In a saucepan over medium heat combine the blueberries, 1/2 cup of water, sugar and the lemon juice. Stir frequently and bring to boil.
In a small bowl, mix the cornstarch with 2 Tbs of cold water. Slowly stir the corn starch into the blueberries, taking care not to crush the blueberries. Simmer until the blueberry sauce is thick enough to coat the back of a metal spoon, about 5 mins.
Remove from heat and gently stir vanilla and lemon zest.
NOTE: If sauce is too thick, slowly add water until you reach the desired consistency. If you have no lemons, you can substitute with juice of an orange and its zest (I prefer lemon)