I've been making cashew butter crunch for years with no problems. However, the last few times I've made it the crunch won't "crunch." The recipe calls for granulated sugar, corn syrup and butter to cook to 290, at which point you stir in the cashews. I do that and then spread it on the cookie sheet but it doesn't become brittle and instead becomes sugary. Maybe my candy thermometer has given up the ghost. But, am I overcooking or undercooking for it to become sugary instead of brittle? Thanks!