• Preheat oven to 350°F/175°C. Spray the bottom and sides of a 9x13 cake pan with baking spray (flour combined with baking spray).

For the Lemon Blueberry Cake:

• In a bowl whisk together the flour, sugar, cornstarch, baking powder, baking soda, and salt. Set aside.
  
• Zest the fresh lemons to create approximately 2 tablespoon of lemon zest. Then juice the zested lemons to create around 1/2 cup of lemon juice. (Reserve 1 teaspoon of lemon zest and 3 tablespoons lemon juice for the glaze)
• In a separate bowl combine vegetable oil, water, yogurt (if using), lemon zest, and lemon juice. Stir to combine. Add wet mixture to the flour mikxture and stir to combine.
  
• Keep the frozen blueberries frozen to the very end. Add a tablespoon or two of the flour mixture and toss until distributed. If using fresh blueberries, no other work needs to be done.
• Spread 1/4 of the plain batter into the prepared pan. Use a spatula to spread it across the pan evenly. Sprinkle a few blueberries over the batter.
• Pour and spread the remaining batter over the top of the blueberries.
  
• Place in the oven on the middle rack and bake for 50 minutes.

For the Lemon Glaze:

• While the cake bakes, prepare the Lemon Glaze by combining powdered sugar with reserved lemon zest and lemon juice. Stir to combine. Add 1 to 2 tablespoons additional lemon juice for a thinner texture. Or you can use vegan lemon frosting.
• When the cake is done, remove it from the oven. Drizzle the glaze over the cake. Allow it to cool for 10 minutes or so.
• Store the cake in the fridge for up to 5 to 7 days. It can be frozen for up to 2 months.