Rhubarb-Berry Jam

Ingredients for 5 Servings

• 3 pounds (1.25kg) rhubarb, trimmed and sliced into 1/2-inch (2cm) pieces
• 2 cups (250g) packed mixed berries, fresh or frozen
• 1 cup (250ml) water or apple juice
• 5 1/2 cups (1kg, plus 100g) sugar
• juice of one lemon
• pinch of salt
• optional: 1 tablespoon kirsch