Preheat your oven to 375°F (190°C). Line your baking sheets with parchment paper or silicone baking mats (this is critical to prevent sticking).
In a large mixing bowl, whisk together the warm melted butter and packed light brown sugar until smooth and glossy.
Stir in the quick-cooking oats, all-purpose flour, and salt until the dry ingredients are moistened.
Add the beaten egg and vanilla extract, stirring until the batter is completely combined and uniform.
Drop the batter by scant half-teaspoonfuls onto the prepared baking sheets. You must leave at least 3 inches of space between each cookie because they spread out significantly.
Bake for 6-8 minutes, or until the cookies are flat, lacy, web-like, and a rich golden brown.
Remove the baking sheets from the oven and let the cookies cool directly on the pan for a full 5 minutes to firm up.
Use a thin metal spatula to carefully transfer them to a wire rack to cool completely.