In a medium saucepan over medium heat, combine sliced strawberries, sugar, and lemon juice. Stir occasionally as the mixture begins to heat and the strawberries release their juices.

Once bubbling, reduce heat slightly and simmer for about 8–10 minutes. Use the back of a spoon or a potato masher to gently break down the strawberries as they soften.

If you'd like a thicker sauce, stir in the cornstarch slurry and simmer for another 2–3 minutes until thickened.

Remove from heat and stir in the vanilla extract, if using.

Let the sauce cool slightly before serving warm, or refrigerate for a chilled topping.