We used a short, squat pecan called the Elliot, which measures approximately 3/4 inch wide. You will need about six times this recipe for the Turtle Cake; the exact amount will depend on the size and variety of the pecans you buy.
Gently insert a toothpick into underside of each pecan; set aside. Spread a sheet of parchment paper on countertop. Spray a large grid-style cooling rack with vegetable-oil cooking spray. Elevate rack over parchment paper, setting it on four same-size cans, one at each corner. This will enable you to cool nuts, once dipped, without marring glaze. Fill a large bowl with ice water, and set aside.
Place sugar and the water in heavy-bottom 2-quart saucepan. Set pan over medium heat; stir until sugar dissolves and begins to simmer. Use wet pastry brush to remove crystals that form on the sides of pan. Do not stir mixture again. Cook over medium heat until sugar turns light amber. Immediately remove pan from heat, and set in ice bath for 5 seconds. This will "shock" the sugar and prevent it from cooking further.
Tilt pan of caramel slightly, and dip the skewered pecans one by one into caramel; set them, toothpick side down, on prepared rack. If caramel begins to harden, causing a thick coating on pecan, gently reheat caramel over low heat. If caramel darkens after reheating a few times, discard and make new batch.
Once pecans have cooled, remove the toothpicks, then remove pecans from rack. Cut away any excess drips or strand of caramel from pecans. Candied pecans can be stored in a single layer in a parchment-lined, airtight plastic container for up to one week.
The recipe should not be doubled, so make each batch one at a time. You'll need a toothpick for each pecan half.