Cookies won't set or are too soft

Cause: The mixture was not boiled long enough. Solution: Boil for exactly 1 minute at a full rolling boil. You can also refrigerate to help them firm up.

Cookies are too dry or crumbly

Cause: The mixture was boiled too long, evaporating too much moisture. Solution: Boil for exactly 1 minute — no longer. If already made, try pressing into a pan with a drizzle of milk.

Cookies are grainy or gritty

Cause: Sugar did not fully dissolve. Solution: Make sure to stir constantly while bringing to a boil, and use standard granulated sugar (not coarse).

Cookies are too sticky

Cause: Not enough oats relative to the wet mixture. Solution: Add more oats, 1/4 cup at a time, until the mixture is scoopable.

Mixture seized or got too thick too fast

Cause: Peanut butter was too cold, or mixture cooled too quickly. Solution: Use room-temperature peanut butter and work quickly after removing from heat.