Preheat your waffle maker according to the manufacturer's instructions (about 3–5 minutes). Lightly brush both plates with melted butter using a pastry brush.
In a large bowl, whisk together the flour, sugar, baking powder, and salt until evenly combined. Make a well in the center of the dry ingredients.
Carefully separate the eggs, placing the yolks in a small bowl and the whites in a clean, grease-free medium bowl. Ensure no yolk gets into the whites.
Whisk the egg yolks, whole milk, neutral oil, vanilla extract, and melted butter together in a medium bowl until fully combined.
Pour the wet ingredients into the well in the dry ingredients and gently stir until just moistened — a few lumps are fine. Do not overmix.
Using an electric hand mixer, beat the egg whites on high speed for 2–3 minutes until stiff, glossy peaks form.
Stir one-third of the whipped whites into the batter to lighten it, then gently fold in the remaining whites using a rubber spatula until just combined with no large white streaks.
Pour approximately ¾ cup of batter onto the center of the iron, close the lid, and cook for 4–5 minutes until steam stops escaping and the waffle is deep golden brown.
Transfer finished waffles to a wire rack on a baking sheet in a 200°F (93°C) oven. Do not stack waffles; re-butter the iron between each pour.
Remove waffles from the oven, add your favorite toppings, and serve immediately for the best texture and flavor.