Insert a 5-inch dowel or nontoxic twig into the stem end of each apple.

Combine sugar and corn syrup in a medium heavy-bottomed saucepan, and stir. Cover, and cook over medium-high heat until sugar melts. Uncover, and continue to cook, swirling occasionally, until mixture is dark golden, about 10 minutes. Slowly drizzle in heavy cream. Remove from heat, and stir until smooth. Transfer caramel to a small metal bowl. Let stand 3 minutes to let caramel thicken slightly, then dip bottom of 1 apple to test if caramel is thick enough. If most of the caramel runs off of apple, let caramel cool 1 to 2 minutes more, then try again.

Dip 3 apples, including test apple, 1 at a time, into caramel to coat three-quarters of each apple. Let excess drip off, and scrape bottom of apples against the side of bowl (if caramel begins to harden, reheat in bowl over a pot of simmering water). Immediately after coating each apple, dip into nuts, using your fingers to help them adhere. Transfer each apple as decorated to a baking sheet lined with parchment or a nonstick baking mat, and let set completely, about 30 minutes.

Coat 3 more apples with caramel as above, this time pressing each with salt flakes along top edge of caramel immediately after coating. Transfer to lined baking sheet, and let set.

Coat the 3 remaining apples with caramel. Transfer to lined baking sheet, and let set.

Place chocolate in a heatproof bowl set over a pan of barely simmering water. Stir until melted and completely smooth. Fill a small resealable plastic bag with chocolate, and snip a tiny hole in 1 corner. One at a time, hold the 3 plain caramel apples horizontally over baking sheet, drizzle with chocolate in a back-and-forth motion, spinning apple as you drizzle. Return to baking sheet to set, about 30 minutes.