Preheat oven to 350 degrees F. Grease and flour a 6 cup Bundt pan.
Sift together flour, baking powder and baking soda, then stir in the salt.
In a mixing bowl, combine the sugar and lemon zest and mix together until sugar is fragrant with lemon. Add the butter and beat with an electric mixer until creamy.
Add the egg and beat for 30 seconds, then add egg yolk and beat for 30 seconds. Beat in the vanilla extract and the vegetable oil. Stir in the buttermilk.
By hand or using lowest speed of mixer, add the flour mixture and stir until blended.
Toss the blueberries with ½ tablespoon of flour and stir into the batter.
Scrape batter into pan and bake at 350 degrees F. for about 40 minutes or until a cake tester comes out clean. Allow the cake to cool for 15 minutes, then turn from the pan
Notes
For the "no butter" version, omit both the butter and the buttermilk and use 6 tablespoons of oil (total) and 6 tablespoons of Greek yogurt.