Ruby red grapefruits tend to get all the glory, but lately I've been relishing the white-fleshed yellow variety thanks to an abundant little grove of grapefruit trees near my mother-in-law's house in Southern California. The best yellow grapefruits have just the right balance of acid and sugar — not too sweet, not too puckery, and with a pleasant trace of bitterness. This makes for excellent marmalade and a nice change of pace from the standard orange kinds.
Growing just around the bend from these particular grapefruits is a cluster of elder trees — the inspiration for this grapefruit and elderflower marmalade. The delicate elderflower pairs beautifully with the citrus in a way that's subtly floral and refreshing. It won't hit you over the head, but it will give the preserves an extra note of warmth and sunshine.
Adapted from Grapefruit Marmalade in Ball Complete Book of Home Preserving
Makes about 3 half-pint jars
1 large white or yellow grapefruit (preferably organic)
Pinch kosher salt
4 cups water, plus more for cooking the peels
3-4 cups granulated sugar
1/4 cup elderflower cordial
Wash the grapefruit. Cut off the top and bottom and discard. Score the peel into quarters and then carefully pull the peel off the grapefruit. Using a metal spoon, gently scrape and discard the bitter white pith from the backside of the peels. Thinly slice the peels. Place the peels in a large non-reactive saucepan, add a pinch of salt, and cover well with water. Bring to a boil over medium-high heat and boil for 10 minutes, periodically pushing the peels down with a wooden spoon. Drain and return the peels to the saucepan.
Working over a bowl, use a sharp knife to separate the grapefruit flesh from the membranes. After removing the flesh, squeeze any juice from the membranes. Add the flesh and juice plus 4 cups of water to the saucepan with the peels. Boil over medium-high heat for 10 minutes, stirring occasionally. Remove from heat, cover, and let stand for 12 to 18 hours.
Bring to a boil over medium-high heat and boil until the peel is tender, about 15 minutes. Remove from heat and measure the fruit mixture (there should be 3 to 4 cups). Measure out an equal amount of sugar. Spread the sugar on a baking sheet and heat it in a 200°F oven until warmed.
Return the fruit mixture to the saucepan and bring to a boil over medium-high heat. Add a small pinch of salt and stir in the warmed sugar. Cook at a rapid boil, stirring frequently, until it reaches a gel set, about 30 minutes. Stir in the elderflower cordial and boil for 30 seconds. Remove from heat and let stand for 5 minutes.
Ladle the marmalade into 3 sterilized half-pint jars, leaving 1/4-inch headspace. Seal and process in a boiling water bath for 10 minutes.