Cook strawberries, sugar, 1/4 cup water, and lemon juice in a saucepan over medium heat, stirring often, for 12-15 minutes (frozen strawberries may take longer) until the strawberries start to break down.
Use a wooden spoon to mash up the strawberries even more. Continue boiling until the sauce has thickened. See Note 1 to make an even thicker consistency.
Remove from heat and stir in vanilla and salt.
Notes
Note 1: Cornstarch
For a thicker consistency, mix together 2 tablespoons of cornstarch and 2 tablespoons of water. Add the mixture to the boiling sauce and stir constantly until it is thickened.
Note 2: Smooth Sauce
For a smoother consistency, puree the cooled sauce in a blender.
Note 3: Food Coloring
You can add a few drops of red food coloring for a deeper red color.
Note 4: Storage
Allow the sauce to cool, and then store it in an airtight container in the fridge for up to a week or in the freezer for up to six months.