Preheat oven to 350 degrees Grease a 9 by 2-inch round cake pan with butter or nonstick cooking spray. Line the bottom with a round of parchment paper and grease the paper. Set the pan aside.
In a medium bowl, sift together the flour, baking powder, and salt.
In a small bowl, combine the sugar and lemon zest. Rub the sugar and zest together with your fingers until fragrant. Pour the mixture into a large bowl. Add the eggs, oil, yogurt, lemon juice, and vanilla extract. Stir until well combined and smooth.
Add the dry ingredients to the wet ingredients and whisk until there are no lumps and the batter is smooth. Gently fold in the blueberries.
Pour the batter into the prepared pan and smooth the top. Bake for 35-50 minutes or until a toothpick inserted in the center comes out clean, and the cake bounces back when lightly pressed. Mine takes around 45 minutes, but check early to be safe. Remove the cake from the oven and let cool on a wire rack for 20 minutes. Run a butter knife around the edges to gently release the cake from the sides of the pan. Turn it out onto a wire rack and carefully remove the parchment paper. Let the cake cool completely.
While the cake is cooling, make the lemon frosting. Sift the confectioner’s sugar into a small mixing bowl. Add the melted butter and the lemon juice. Whisk together until smooth.
When the cake is cool, pour the frosting onto the center of the cake. Smooth with a spatula or butter knife. Garnish with fresh blueberries, if desired. Cut into pieces and serve.