In a heavy saucepan simmer the strawberries, uncovered, in the water for 15 minutes. Put through a vegetable mill, then stir in the sugar and the potato starch, which has been dissolved in the lemon juice.
Rinse out the saucepan and return the puree to it. Cook for just 2 to 3 minutes, until thickened. Stir in the almond extract, then pour into a bowl and let chill in the refrigerator.