Preheat oven to 350 degrees. Grease and flour a 9x5 inch loaf pan.
Melt the butter in the microwave in a large mixing bowl, set aside to cool slightly for about 5 minutes.
To the butter add the eggs, sugar, Greek yogurt, lemon juice, lemon zest, and vanilla extract. Mix using a hand mixer for 2-3 minutes until well combined.
In a small bowl whisk together the flour, baking powder, and salt.
Add the dry ingredients to the wet and use a spatula to stir just until combined.
If desired, toss the blueberries with the cornstarch, then mix into the batter. You can also skip this step and stir the blueberries in if you don't have cornstarch.
Bake in preheated oven for 45-60 minutes.
Remove the pan from the oven and allow the cake to sit for 10 minutes before gently removing from the pan to a wire rack. Cool completely before glazing.