- 3 pounds ripe beefsteak tomatoes, peeled and chopped, reserving any juices
- 3 cups sugar
- 2 juice oranges, quartered, seeded, and sliced crosswise 1/8 inch thick
- 1 lemon, quartered, seeded, and sliced crosswise 1/8 inch thick
- 1/8 teaspoon salt
- Special equipment: 3 (1/2-pint) canning jars (optional) with lids and screw bands; a wide 5- to 6-quart heavy pot (at least 9 1/2 inches in diameter)
- If desired, sterilize jars , lids, and screw bands.
- Chill 2 small plates (for testing marmalade).
- Cook all ingredients, including reserved juices from tomatoes, in pot over moderate heat, stirring frequently, until sugar is dissolved, about 6 minutes. Simmer, stirring frequently as marmalade thickens (to prevent scorching) and adjusting heat as needed, until marmalade tests done, 50 minutes to 1 1/4 hours. Begin testing for doneness after 50 minutes: Drop a spoonful of marmalade on a chilled plate, then tilt; it should remain in a mound and not run (if necessary, remove pot of marmalade from heat while testing).
- If not processing, cool marmalade, uncovered, then chill in an airtight container (preferably glass).
- If processing, drain jars upside down on a clean kitchen towel 1 minute, then invert. Ladle marmalade into jars, leaving 1/4 inch of space at top. Run a thin knife between marmalade and jar to eliminate air bubbles.
- Seal, process, and store filled jars (and boil marmalade in jars 10 minutes).
- Let marmalade stand in jars at least 1 day for flavors to develop.