A mix with red and blackcurrants will help the set as these berries contain the most natual pectin. Put the ingredients in a pan and let sit for an hour or so until the berries defrost
Heat on a low setting to dissolve the sugar, stirring occasionally
Heat your oven on it's lowest setting - gas 1 / 100C / 220F. Wash a couple of jars in hot, soapy water then set them upsides down on the oven rack to sterilize them. Done when dry
Once the sugar has completely dissolved, crank up the pan heat and bring to a rolling boil
If using a jam thermometor, set occurs at 105C / 221F. I use the wrinkle method. Every few minutes, spoon some of the jam onto a cold plate. If you can push the jam with your finger and it wrinkles up, it's reached setting point
Once this happens, turn the pan off and let sit for 10 minutes to thicken slightly so the fruit doesn't all sink to the bottom or float to the top once it's in the jars. I mashed the bigger blackberries up with a fork too
Fill the jars and put the lids on. The heat within will vacuum seal them. Let them stand on a wire rack until cooled, then enjoy!
