Preheat your Belgian waffle iron to medium-high heat. While it heats, place a cooling rack nearby to keep finished waffles crispy.
Carefully separate the eggs, placing whites in a clean dry bowl and yolks in a small bowl. The egg whites must be in a completely grease-free bowl.
In a large bowl, whisk together the gluten-free flour blend, tapioca starch, granulated sugar, baking powder, and salt until evenly combined.
In a separate medium bowl, whisk the egg yolks, milk, neutral oil, and vanilla extract until smooth and fully combined.
Using a hand or stand mixer, beat the egg whites on medium-high speed until stiff peaks form, about 2-3 minutes. Do not skip or rush this step.
Pour the wet ingredients into the dry ingredients and stir with a spatula until just combined. A few small lumps are fine. Do not overmix.
Fold one-third of the whipped egg whites into the batter to loosen it, then gently fold in the remaining whites with an under-and-over motion until just incorporated.
Lightly coat the preheated waffle iron plates with cooking spray or melted butter using a pastry brush or paper towel.
Pour about 3/4 to 1 cup of batter onto the hot waffle iron and close the lid. Cook for 4-6 minutes until steam stops escaping and the waffle is golden brown.
Carefully transfer the finished waffle to a cooling rack to keep it crispy. Re-grease the iron and repeat with remaining batter.