Place a folded kitchen towel in the bottom of an 11-inch straight-sided sauté pan. Add about an inch of water to the pan and place over medium heat until it reaches a bare simmer, around 190°F. You should see steam rising and tiny bubbles forming, especially around the edges. You’ll want to maintain this temperature throughout the process, so keep your thermometer handy and be prepared to drop the heat if the water starts to boil.
Combine the chocolate, cream, coffee, corn syrup, and salt in a glass or metal heat-safe bowl that fits comfortably inside the sauté pan. Place the bowl directly on the towel and let sit in the water, stirring frequently with a rubber spatula, until the chocolate is almost (but not quite) melted, 3 to 5 minutes. Then remove the bowl, place it on the counter, and stir until the mixture is smooth.
Take the temperature of the chocolate. If it’s between 88 and 90°F, it’s workable. If it’s over, just park the bowl on the counter for a few minutes, temping often until it’s in the zone. To glaze, quickly dip the long side of an éclair into the mixture, lift, and drain for a count of three, then flipIt’s all in the wrist. right-side up.
Transfer to a platter, refrigerate until chilled, and serve.