Grease and line a 7-inch round and deep cake pan with baking paper.
Add olive oil, lemon zest, lemon juice, eggs and caster sugar to the bowl of an electric mixer. Beat for 3-4 minutes until pale, creamy and voluminous.
Add flour and ricotta cheese. Mix very gently with a wooden spoon until the batter is just combined, ensuring there are small lumps of ricotta intact in the batter. At this point if you feel the batter is too stiff (it should be the consistency of a thick paste but not soft and runny), you made add 2-3 tablespoons milk of choice to loosen it up in order to get the perfect crumb after baking.
Bake in the preheated oven for 50-55 minutes until golden and cracked on top.
Remove from oven. Cool for 10 minutes. Dust with icing sugar, cut and serve.
Homemade Ricotta - You can make this cake with homemade ricotta. Use full-fat, creamy milk to make ricotta. Bring two liters of milk to a gentle boil on medium-low. Add 2 teaspoons of sea salt flakes and mix well. Add 4 tablespoons of lemon juice. Stir and agitate the milk. The milk will curdle. Give it one last gentle mix, remove from heat and cover and rest for 30 minutes. Line a sieve/ricotta basket with two layers of cheesecloth. Place this over a bowl. Pour the curdled milk into the cheesecloth-lined basket. Allow the ricotta to drain for 8-10 hours in the fridge or in a cool corner of your kitchen (if it is winter). Turn the drained ricotta out into a large lidded glass container. Store in the fridge for upto two days and use it up.
Store-bought ricotta - Don't use smooth ricotta. Use the traditional ricotta that is grainy and has beautiful texture.
When mixing ricotta into the cake, only mix gently while leaving textural lumps in the batter. This makes for a delightfully textural cake (like the one pictured here). For a smoother cake, mixing the ricotta in a bit more.
* The decision to use milk is a matter of the consistency of ricotta. If you use homemade ricotta, you don't need to use additional milk in the batter. This is because homemade ricotta is softer and less firm than store-bought ricotta. If you are using store-bought ricotta and you find that your batter is too stiff (i.e it is a very stiff paste consistency and doesn't swirl easily with the spoon, then you can loosen it up by adding 2-3 tablespoons of milk of choice. This will ensure that the final cake is not too dry and has a good crumb).
Don't skimp on the lemon zest and juice. They are the star of the show.