Combine milk, sugar and butter in a large saucepan over medium heat; boil. Stir in strawberries and lemon juice. Heat, stirring constantly, to between 234 and 240 degrees F (112 to 116 degrees C), or until a small amount of syrup dropped into cold water forms a soft ball that flattens when removed from the water and placed on a flat surface.
Remove from heat and quickly spread in prepared pan. Let cool before cutting and serving.