In a medium saucepan, combine sliced strawberries, sugar, and lemon juice. Place over medium heat and bring to a boil, stirring occasionally. Strawberries will release their juice without any mashing required.n2. In a small bowl, whisk the cornstarch and warm water together until dissolved. Add to the saucepan once the mixture is bubbling.n3. Reduce heat and let it simmer for 15-20 minutes or until the sauce thickens, stirring occasionally. Remove from heat and cool to room temperature, keeping in mind that sauce will thicken more as it cools. Serve warm or refrigerate for later.n