In a medium saucepan over medium heat, combine the butter, granulated sugar, milk, lemon zest, and fresh lemon juice. Stir continuously until the butter melts and the mixture begins to bubble.
Let the mixture gently boil for one full minute while stirring constantly. This helps dissolve the sugar completely and blend the citrus oils.
Remove the saucepan from heat. Stir in the vanilla extract and a pinch of salt. These ingredients deepen the flavor profile and balance the tartness.
Add the old-fashioned oats to the saucepan. Stir until all the oats are evenly coated with the lemon-sugar mixture.
Using a spoon, drop rounded spoonfuls of the oat mixture onto a baking sheet lined with parchment paper. Try to keep them consistent in size for even setting.
Let the cookies sit at room temperature for 30 to 45 minutes, or until they are firm to the touch. No refrigeration required!
