Preheat the oven to 170 degrees celsius and pre-line a 20cm baking tin.
In a large mixing bowl, combine the lemon zest and sugar and rub the two together with your fingers to flavour the sugar. Add the eggs and whisk until pale, smooth and frothy.
In the same bowl, combine the lemon juice, olive oil, ricotta and vanilla essence and whisk until all ingredients are well combined. Sift in the flour and baking powder and gently combine the wet and dry ingredients with a spatula. Add 1 punnet of blueberries and gently fold through.
Transfer the cake batter to the baking tin and smooth out on top with a spatula. Scatter the remaining blueberries on top and push them into the batter so their tops are slightly exposed.
Bake for 50 minutes or until golden on top and a skewer comes out clean when poked into the middle. Leave to cool for 15 minutes in the tin then transfer to a cooling rack. Serve on its own or with ice cream.