Dissolve 1 cup sugar in 2 cups water by heating gently. Cool; add ascorbic or citric acid mixture. Peel and slice apples 1/4 inch thick into the sugar-water-acid solution. Gently boil the apples in the solution for 5 minutes. Remove from heat and let the apple mixture sit for 10 minutes. Combine the remaining 1/2 cup sugar, cornstarch, and salt. Mix with 1/2 cup water until a smooth paste is formed. Slowly add this paste to the apple mixture and stir just enough to disperse the starch throughout. Stir in lemon juice, if needed. Bring the apple filling to a boil and hold for 1 minute. Immediately put into jars. Place lids, and secure on bands firmly. Process in a boiling water bath or steam canner for 40 minutes at sea level (add 2 minutes of processing time for each 1000 feet above sea level). (Recipe courtesy of Utah State University Extension.) Note: The initial 1 cup sugar may be increased or decreased by 1/4 cup without affecting the processing time. To avoid an unsafe product, do not change the other proportions in the recipe. Do not attempt to double or triple the recipe.