Rinse the strawberries and rhubarb with cold water, then pat dry using kitchen paper.
Hull the strawberries, then cut them into cubes together with the rhubarb.
Add them to a large mixing bowl together with the sugar, and toss everything well to combine.
Set aside for 20-30 minutes for some liquid from the fruit to be released.
Transfer the mixture to a pan set over a low to medium heat, and leave it to simmer until the fruit is soft and mushy, but there is still some liquid left - this will set further once the jam cools down completely.
Preheat the oven to 200 degrees Celsius (390 Fahrenheit).
Rinse and dry 2 small jam jars, and place them onto a tray.
Transfer them into the oven for 10 minutes to be sterilised.
Carefully remove them from the oven with an oven glove or kitchen towel, and pour the hot jar into the jars.
Tighten the lids very well, then place the jars upside down and allow them to cool down completely.