Macerate the fruit: Combine the 1 pounds strawberries, hulled and chopped and 1 pounds rhubarb, trimmed and chopped into small pieces with the 2 cups granulated sugar and 2 tablespoons fresh lemon juice in a large bowl. Stir well, cover, and let sit at room temperature.

Cook it down: Transfer the fruit, sugar, and all released juice to a wide, heavy-bottomed pot. Add the 0.1 teaspoons salt. Bring to a boil over medium-high heat, stirring often to prevent scorching.

Simmer to set: Reduce heat slightly and simmer, stirring frequently, until the jam thickens and reaches about 220°F on a candy thermometer.

Do the spoon test: Drop a spoonful of jam onto a plate that's been chilled in the freezer. Run your finger through it — if it wrinkles and holds its shape, it's ready.

Jar it up: Ladle the hot jam into clean jars, leaving about ¼ inch of space at the top. Let cool to room temperature before sealing and storing.