Excerpted from Put 'Em Up! by Sherri Brooks Vinton (Storey/the book). Copyright ©2010. Used with permission.
Yield: About 3 cups
Combine the lemon zest, juice, sugar, butter, eggs and salt in the top of a nonreactive double boiler. Bring the water in the bottom pan to a low boil and whisk the curd constantly until it thickens, about 10 minutes. Strain through a fine-mesh sieve.
To refrigerate: Ladle into bowls or jars. Cool, cover and refrigerate for up to 2 weeks.
To can: Use the boiling-water method. Ladle into clean, hot 4-ounce or half-pint canning jars, leaving ¼ inch of headspace. Release trapped air by running a chopstick or butter knife around the inside edge of the canning jar. Wipe the rims clean, center the lids on the jars and screw on jar bands. Process for 10 minutes. Turn off the heat, remove the canner lid and let the jars rest in the water for 5 minutes. Remove jars and set aside for 24 hours. Check the seals, then store in a cool, dark place for up to 1 year.