In a large mixing bowl, combine chopped rhubarb and strawberries with granulated sugar. Stir to coat the fruit with sugar.

Cover the bowl with plastic wrap and refrigerate for 12 to 24 hours.

Wash canning jars in hot, soapy water and rinse. Place in simmering water to warm.

Transfer the fruit mixture to a large pot. Add bottled lemon juice and a pinch of fine salt.

Bring to a boil over medium-high heat, stirring occasionally. Cook for about 25 minutes until the jam thickens.

Test for set point using a cold plate. Drop a spoonful onto the plate; it should slide off in a sheet.

Carefully remove jars from hot water. Fill each jar with jam, leaving 1/4 inch headspace.

Lower filled jars into boiling water and process for about 10 minutes.

Allow jars to cool for 24 hours. Store in a cool, dark place.