Heat a large non-stick saucepan on the lowest possible heat on your hob.
Put the egg yolk, sugar, plain flour and baking powder into a large mixing bowl and whisk together. Whisk in the milk, and then the oil, to give a smooth, thick paste.
In another large bowl, use an electric hand whisk to bring the egg whites to soft peaks. Add the cream of tartar and caster sugar, and whisk to firm peaks.
Spoon ¼ of the egg whites into the batter mix and use a whisk to combine. Add half of the remaining egg whites and use a whisk to gently fold the mixture together, until the egg whites are 3/4 mixed through. Add the remaining egg whites and gently fold with the whisk again, until the egg whites are again 3/4 mixed through. Switch to a spatula for the last few folds, until the mixture is just combined.
Add a small amount of vegetable oil to the pan and wipe most of it out with a piece of kitchen towel. Use half of the pancake mixture to place 3 large spoonfuls, well spaced out, in the heated pan. Sprinkle two teaspoons of water into the pan (not on the pancakes, but in the gaps around them), put the lid on and time for 5 minutes. After 5 minutes are up, take the lid off and spoon the remaining batter on top of the semi-cooked pancakes. Add another two teaspoons of water to the pan and put the lid on for another 5 minutes. When that time is up, remove the lid and carefully flip the pancakes over with a spatula and small palette knife. Add another two teaspoons of water and place the lid back on for 10 minutes.
After 20 minutes in total, the pancakes will be cooked through. Serve immediately, topped with maple syrup and blueberries.