Preheat and Prepare: Turn on your waffle iron to preheat according to the manufacturer's instructions. In a large mixing bowl, whisk together the plain flour, caster sugar, baking powder, and salt. Creating a well in the centre can make the next step a little easier.

Mix the Wet Ingredients: In a separate medium-sized bowl, whisk the two egg yolks until they are pale and slightly frothy. Whisk in the whole milk, the slightly cooled melted butter, and the vanilla extract until everything is well combined.

Combine Wet and Dry: Pour the wet mixture into the well of the dry ingredients. Whisk everything together until it is *just* combined. I find that it's crucial not to overmix here; a few small lumps in the batter are perfectly fine and actually desirable. Set the batter aside for a moment.

Whip the Egg Whites: In a clean, dry bowl (I prefer metal or glass), use an electric hand mixer or a stand mixer to whisk the two egg whites. Start on a low speed and gradually increase to high. Continue whisking for 3-4 minutes, or until stiff peaks form. This means when you lift the beaters out, the peak of egg white holds its shape without flopping over.

Fold in the Whites: Take about one-third of the whipped egg whites and gently fold them into the batter using a spatula. This lightens the batter, making it easier to incorporate the rest. Add the remaining egg whites and fold gently until just combined. You want to see some streaks of white remaining – be careful not to deflate all that lovely air you just created.

Cook the Waffles: Lightly grease your preheated waffle iron if required. Ladle the recommended amount of batter onto the iron (check your manual, but it's usually around 120-180ml per waffle). Close the lid and cook for 4-6 minutes, or until the waffle is a deep golden brown and crisp. The steam will have mostly stopped coming out of the sides.

Keep Warm and Serve: Carefully remove the cooked waffle and place it on a wire rack set inside a baking sheet in a low oven (around 100°C) to keep warm and crisp while you cook the remaining batter. Serve hot with your favourite toppings.