In a medium saucepan, combine sliced strawberries, sugar, and lemon juice. Stir well to combine.n2. In a small bowl, mix the cornstarch with 2 tablespoons of water until smooth. Add it to the strawberry mixture along with the vanilla extract.n3. Place the saucepan over medium heat and cook until the mixture comes to a boil, stirring occasionally.n4. Reduce heat and simmer for about 5-10 minutes, or until the strawberries are soft and the sauce has thickened slightly.n5. Remove from heat and let cool slightly. Serve warm or refrigerate until cool before using.