Preheat the oven to 350°F. Peel the top third of the apples and core. Put the sugar, water, salt, and lemon zest in a small pan, bring to a boil, stir, and remove from the heat.
Set the apples upright in a baking dish and pour the syrup over. Cover (use foil if there is no lid that fits) and bake for about 30 minutes, or until the apples are easily pierced with the tip of a knife.
Spoon some of the syrup over the apples and sprinkle a little sugar over the top. You may put them under the broiler for 2 to 3 minutes to brown.