In a medium saucepan over low/medium heat, add 3 cups of frozen strawberries. As the strawberries begin to melt, pour 2 tablespoons of the strawberry liquid into a small bowl. Stir 2 teaspoons corn starch into the liquid until dissolved and set aside.
Add 1/4 cup maple syrup, 1 teaspoon lemon juice, and 1 teaspoon vanilla extract to the saucepan with the strawberries and bring to a low simmer for ten minutes, stirring occasionally.
Use a fork or potato masher to gently mash the strawberries to your preferred texture—smooth or chunky, it’s up to you! You can pour the mixture into a blender if you would like it extra smooth. Then, return it to the saucepan over low/medium heat.
Pour in the cornstarch slurry and allow to simmer for 2 minutes until thickened. Stir frequently to keep it from sticking to the bottom of the saucepan. Remember, it will keep thickening as it cools.
Take the pan off the heat and let the jam cool. Pour it into a glass jar or container and pop it in the fridge.