*loosely adapted from Williams Sonoma
Yield: ~ 1-3/4 cups
4 lemons (or ~6 Meyer lemons), or 2 oranges, or 5 limes (or ~8 Key Limes), preferably organic
2 whole eggs plus 4 egg yolks
1 cup sugar (200 grams) (7 ounces)
4 tablespoons (60 grams) (2 ounces) unsalted butter, at room temperature and cut into small even cubes
1. Wash citrus really well (with a bristled brush under cold water) and using a Zester, remove all of the coloured portion of the peel from the fruit (not the white pith--it's quite bitter!) into a bowl or onto a piece of wax paper. Rotate fruit as necessary to get as much of the zest off. Repeat until you have 2 teaspoons (30 mL) of the zest, and set aside.
2. Slice the citrus in half crosswise (I find room temperature citrus is best for juicing) using a sharp knife, and extract as much of the juice as you can using a citrus reamer, or I use a small Citrus Juicer. Just be sure to catch all of the juice in a bowl and to completely strain the seeds before using. Repeat the juicing until you have 2/3 cup (5 fl oz/160 mL) of the strained juice.
3. Get your double boiler ready by filling a saucepan with 1" of water, then placing a metal bowl on top of the saucepan. You will need to ensure the bowl fits snugly into the top of the saucepan and that the bottom of the bowl doesn't touch the water (important, or your eggs will cook!). You can now remove the bowl and continue with making the curd.
4. Whisk the juice, whole eggs, egg yolks and sugar in the bowl until smooth. Add the butter cubes to the bowl, but don't stir.
5. Heat the water in the saucepan over low heat until it simmers (not boils) and place the bowl atop the rim. Stirring gently, but constantly, using heatproof spatula or wooden spoon, cook until the curd has thickened and all of the butter has melted and is incorporated, about 10 minutes (this can vary). To test if the curd is thick enough, remove the spatula or spoon from the curd and check that it's coated.
6. Strain the curd over a bowl using a fine-mesh sieve and then stir in the zest. Cover with plastic wrap pressed directly against the curd (to prevent a skin from forming) and chill for at least 3 hours (I like to chill it overnight). It also thickens up a bit more while chilling.
You can use the chilled curd right away, keep in an airtight container in the refrigerator for up to 3 days, or freeze the curd in an airtight container with plastic wrap pressed directly onto the curd surface for up to 1 month. To use frozen curd, you can remove from freezer and use immediately--no need to thaw it as it doesn't really freeze, per se. You can either scoop out what you need and keep the rest in the freezer or use all at once.