Place strawberries in a large pan with granulated sugar and cook on medium heat, stirring often, until berries are softened and there is a lot of juice in the pan, this took about 20-25 minutes for me.
Stir together corn starch and water and add to the strawberries while it is still on the heat. Stir until thickened and remove from the heat.
Stir in vanilla and let cool slightly before serving warm, or let cool to room temperature and refrigerate to serve later.