A 9-inch pie plate
Glass or ceramic, 9 inches across, is what this recipe is written for. A glass plate (for example from Pyrex) lets you see whether the crust is browning. 9-inch pie plate.
Key limes versus Persian limes
The Key lime (often sold as Citrus aurantifolia, sometimes called the Mexican or West Indian lime) is small, rounder than a regular lime, thinner-skinned, and more aromatic. It is often more yellow than green when it is fully ripe. The ordinary lime in most U.S. grocery stores is the Persian lime (Citrus × latifolia): larger, seedless or nearly so, thicker-skinned, and usually sold deep green. Persian limes make a perfectly decent lime pie, but they are less floral and a bit less sharp than Key limes, which is why the name on the dessert matters.
Fresh Key limes can be uneven in stores, especially outside Florida and outside the late-summer and fall window. Bottled Key lime juice is a fair and very common substitute when the label actually says Key lime. Nellie & Joe’s Famous Key West Lime Juice is the well-known Key West brand (Nellie & Joe’s Key West Lime Juice on Amazon).
Tools worth having
Citrus press or juicer
Key limes are small and seedy. A handheld citrus press or lime juicer is much faster than squeezing them with your fingers, and you will need a good number of fruits to make 150 ml of juice.
A fine zester
If you have fresh Key limes, a fine citrus zester gets the fragrant outer peel without the bitter white pith. Zest is optional when you are using bottled juice.
Graham crackers for the crust
About 10 full sheets, crushed, make 1½ cups of crumbs. graham crackers. A pastry crust is more traditional in some older Key West recipes; graham is the usual home version now.
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