Use fresh lemon juice for the best flavor; bottled juice can make the bars taste metallic.
For easier cleanup, line the pan with parchment paper, leaving an overhang on the sides to lift the bars out.
Store leftovers in an airtight container at room temperature for up to 3 days, or refrigerate for up to a week.
These bars freeze well. Wrap tightly in plastic wrap and foil before freezing for up to 3 months.