Add the Saskatoon berries, sugar and 1 cup of water to a small pot on medium heat.
Bring to a boil, then boil for 5 minutes while stirring occasionally.
Once boiled for 5 minutes, add the cornstarch and 2 Tablespoons of cold water to a small bowl and mix until combined.
Slowly pour cornstarch mixture over the Saskatoon berry mixture while stirring.
Stir in the lemon juice.
Reduce heat to medium low and continue cooking for about 15 minutes, until thickened. Make sure to stir occasionally.
Remove from the heat and pour into a 500 ml mason jar or cool slightly and transfer to an air tight container then place in the fridge to continue thickening, or serve warm.
Notes
Once cooled, store in the fridge in an airtight container or 500ml mason jar for up to 1 week.To freeze add sauce to a freezer safe container or freezer bag once completely cooled, thaw in the fridge.