You really only need 5 items to make these lemon bars: gluten-free flour (the all-purpose kind), sugar, butter, eggs, and some lemons. With this last ingredient, you’ll need quite a bit of juice — ½ cup in all, something Brookes says may require you to juice 3 or 4 lemons. Before you cut into them, though, be sure to zest enough of the lemon peel to make up 1 tablespoon, as you’ll be needing this, as well.
A brief note on the lemon zest: there’s no need to run out and buy a dedicated zester, microplane or otherwise. Brookes tells us “I use the small side on the box grater,” and provides us with a tip: “To prevent wasting zest, you can scrape a knife along the inside of the grater to try and get as much of the zest out as possible.”