Preheat the oven to 350 degrees. Butter the sides of a 9 inch round sponge cake pan and set aside.
To make the blueberry topping:
In a small saucepan add the butter, sugar, lemon zest and lemon. Cook for about 2 minutes until the mixture starts to bubble. Stir in the blueberries and pour into the bottom of your prepared pan.
To make the cake:
In a medium sized mixing bowl whisk together the flour, baking powder and salt. Set aside.
In a stand mixture add butter and sugar. Beat together until fluffy about 2 minutes. Add in the eggs one at a time, followed by lemon zest, vanilla, and lemon extract. Add in the dry ingredients and continue to mix until combined.
Add the batter to the top of the blueberry mixture and spread evenly on the top. Bake for 45-50 minutes or until cake is firm to the touch. Let cake rest for 10 minutes and then flip over and serve.