Preheat your oven to 180°C (350°F) conventional (see note 2 if using a convection oven with a fan) and lightly grease six 6-ounce (3.5-inch wide) ramekins. If your ramekins are shorter, you may get one or two extra puddings—just reduce the bake time slightly.
In a large bowl, combine the egg yolks, sugar (¾ cup – 150g), melted butter, oil, milk, lemon zest, lemon juice, and vanilla. Using a whisk, mix until smooth and well combined.
Add in flour, cornstarch, and salt, and whisk again until just combined. There is no need to sift the dry ingredients. Set mixture aside.
In a clean medium-sized bowl, whip the egg whites using a hand or stand mixer on medium speed for about 30 seconds, until frothy. Gradually add in sugar (¼ cup – 50g) and continue whipping for about 3 minutes, or until soft peaks form. The mixture should look glossy, and the peaks should fold over when lifted (we don't want stiff peaks).
Add half of the whipped egg whites to the egg yolk mixture and using a spatula, gently fold until just combined. Add the remaining egg whites and fold again until just combined, being careful not to deflate the mixture.
Evenly divide the batter between your prepared ramekins, filling them almost to the top with just a small gap.
Place the ramekins in a 9x13-inch pan, then pour hot water into the pan until it comes halfway up the sides of the ramekins. Be careful not to get any water in the batter. You can do this step while the pan is in the oven to avoid carrying hot water (see video for demonstration).
Bake for 23–25 minutes, or until the tops are puffed and lightly golden. The tops should feel just set when gently touched.
Carefully remove the ramekins from the water bath (I use tongs to do this) and place them on a wire rack to cool for about 15 minutes.
Serve warm, either on their own or with a dusting of powdered sugar. Fresh berries or whipped cream work great as well!