For the Crust
- 5 tablespoons unsalted butter, melted and cooled, plus more for the pan
- 1 cup shelled pistachios
- 1 cup (4 ounces) graham cracker crumbs
- grated lime zest from 3 key limes
For the Filling
- 3 large egg yolks
- 1 can (14 ounces) sweetened condensed milk
- 1/2 cup fresh lime juice
- 1 or 2 tablespoons of grated coconut
- Preheat the oven to 350° F. Brush an 8-inch square baking dish with melted butter, and line the bottom with parchment paper. The butter will hold the paper in place. Cut the parchment paper 8 inches wide and at least 12 inches long, so that it hangs over the sides of the pan. This will help lift the bars out easily. It's important to have the parchment in place, otherwise, the dessert won't lift out of the pan. Also, do use an 8-inch baking dish, because there won't be enough topping if the pan is larger.
- Break up the graham crackers into small pieces and add them to a food processor. Add the pistachios and the lime zest. Grind finely and then blend in the butter.
- Press the mixture into the bottom of the prepared pan.
- Bake until lightly browned, about 10 minutes.
- In a large bowl, whisk together the egg yolks and the condensed milk. Add the lime juice and whisk until smooth.
- Pour the filling onto the cooled crust and carefully spread to the edges. The filling will be a thin layer, but it will puff up during baking.
- Bake until set, about 15 to 20 minutes. Halfway through baking, take the pan out and sprinkle the coconut over the top, then continue to bake.
- When done, cool in the pan for 30 minutes. Then, move to the refrigerator and chill for at least one hour before serving. Once you're ready to serve, use the parchment paper overhang and lift the dessert out of the pan. Transfer to a cutting board and using a serrated knife cut into 16 squares, wiping the knife with a paper towel between each cut.
These key lime squares are based on a recipe by Martha Stewart.