• Preheat oven to 325 degrees.
• Zest the limes and then juice them.
• Process the graham crackers in a food processor or blender, then melt the butter and have it ready.
• Whisk the egg yolks and lime zest together in a bowl until tinted light green. This takes about 2 minutes.
• Beat in milk, then juice, and set aside at room temperature till it thickens.
• Mix the graham cracker crumbs and sugar in another bowl.
• Add butter and stir with a fork until well blended.
• Pour this mixture into a 9-inch pie pan and press over the bottom and up the sides of the pan. Try using the bottom of a measuring cup to make sure the graham cracker mixture forms a firm crust on the bottom of the pie pan.
• Bake on the center rack for about 15 minutes until the crust is lightly brown; remove, and let cool to room temperature.
• Pour the lime filling into the crust, spread evenly, and then bake for 15 minutes until the center sets, but still wiggles when shaken.
• Remove from oven and cool to room temperature.
• Refrigerate for at least three hours until well chilled.

Some of you might like to serve it with a whipped cream topping or a meringue topping, but I prefer keeping it simple. If the pie seems to be sticking to the pan when serving, try dipping the pan into a bowl of warm water to loosen it.