Wash and pat the cherries dry.
Remove the stems and pit them.
Cut the cherries into half and place them in a saucepan.
Add sugar and lemon juice.
Add 4 tablespoons of water.
Cook the cherries over low heat until they become soft. Keep the heat low to prevent the sauce from drying out. Also, stir the fruits sauce constantly to avoid the bottom from burning.
Turn of the heat as the fruits become soft. Let them cool down slightly.
Transfer the fruits into a blender and add another 4 tablespoons of water. The water will help the sauce to dilute and this will help with the pulsing of the fruits. Pulse the cherries along with the syrup and water for about 10 to 15 seconds.
Strain the pulsed fruits in a sieve. Use the back of a spoon to press all the fruits extract, leaving behind only the skin.
Remember to scrape the bottom of the strainer as there will be thick cherry sauce remaining there as you press the fruits with the back of the spoon.
Return the strained coulis to the saucepan.
Mix the cornstarch with the remaining water until smooth. Pour the cornstarch solution into the saucepan.
Turn on the heat to low and stir the coulis quickly to disperse the cornstarch. This will prevent it from turning into a gooey clump in the sauce.
Continue to cook the cherry coulis until it thickens and reaches the consistency you desire.
Turn off the heat and let it cool down before pouring into a clean mason jar or a bottle with lid.
Keep the cherry coulis refrigerated.