In a bowl, prepare the cornstarch slurry by dissolving 1 teaspoon of cornstarch in 2 teaspoon of cold water and keep it aside.
If using fresh strawberries, wash them and roughly chop them.
Then in a saucepan on medium heat, add the strawberries and sugar and let it simmer.
Note: If using frozen strawberries, a lot of water will be released initially. This is normal as the strawberries are defrosting. Slowly that water will reduce.
Keep stirring slowly while the strawberries cooks in the sugar syrup. Mash them gently with the spatula.
Cook until the strawberries have softened and there is still some sauce left.
Immediately add the vanilla, lemon juice and the cornstarch slurry. Cook for 30 seconds only and then remove from the heat. The sauce will have thickened.
Allow it to cool and refrigerate.
When ready to serve, add the berry sauce over the panna cotta and garnish with fresh mint.