Line a baking sheet with parchment paper or silicone mat.

In a medium saucepan, combine sugar, butter, and milk. Bring to a rolling boil over medium heat, stirring constantly. Boil for exactly 1 minute.

Remove from heat and stir in lemon zest, lemon juice, vanilla extract, and salt.

Stir in oats until thoroughly coated. Fold in optional white chocolate chips or coconut if using.

Using a tablespoon or cookie scoop, drop rounded portions onto prepared baking sheet and flatten slightly.

Let set at room temperature for 15 minutes, then refrigerate for 15 minutes more until firm.