1) To make the caramel: Place the sugar in a 2-quart heavy saucepan (preferably light colored). Add the water and salt. Cook over medium heat, stirring once or twice, until the sugar is dissolved. Bring to a boil, and cook without stirring until the sugar begins to caramelize (become light to medium brown), which will take about 8 minutes. If using a thermometer, cook the sugar until it's between 350°F and 360°F.
2) Remove the pan from the heat and slowly pour in the heavy cream; the mixture will boil up, so be careful. Return the pan to the heat and stir until smooth. Use more cream for a thinner sauce, the smaller amount if you want it thicker.
3) To prepare the walnuts: Place a medium skillet over medium heat. Melt the butter and add the walnuts. Cook, stirring occasionally, until the nuts are barely starting to brown; this can happen quickly, so keep an eye on them. Sprinkle the sugar over the nuts and stir; add the boiled cider or maple syrup and stir again to coat the nuts. Sprinkle with salt and a pinch of cayenne. When the nuts are coated, remove from the heat and spread on a baking sheet or piece of parchment to cool.
4) To make the biscuits: Preheat the oven to 425°F. In a medium bowl, whisk together the self-rising flour and brown sugar. Work in the butter until it's in small pieces. Combine the boiled cider with the smaller amount of milk and add to the flour mixture, stirring until the flour is evenly moistened. Dribble in more milk, if necessary, to bring the dough together. Use a bowl scraper to fold the dough over on itself a few times to bring it together.
5) Turn the dough out onto a piece of parchment paper, pat it into a 6" to 6 1/2" circle (about 3/4" thick), and cut into circles with a 2" cutter. Pile any scraps on top of each other, fold twice to bring them together, and cut the remaining dough; you should get 8 to 10 biscuits.
6) Place the biscuits on a baking sheet, leaving 2" between them. Bake for 14 to 16 minutes, until they're light golden brown. Remove them from the oven, and keep warm.
7) To prepare the apples: While the biscuits are baking, place a skillet over medium heat. Add the butter, and when it's melted, add the apples and spices. Cook for 2 minutes, stirring occasionally, then add the caramel sauce and boiled cider. Cook for 1 minute more, then remove from the heat.
8) To assemble: Split the biscuits, and spoon 5 to 6 apple slices over the bottom half of each. Drizzle with some caramel sauce, then place the tops of the biscuits over the apples. Add a scoop of ice cream, more caramel sauce, then sprinkle with spiced walnuts.
Yield: 8 to 10 servings.