First, a couple of notes on cooking with lavender:
-The leaves as well as the flower blossoms are edible.
-If you don't grow it yourself, make sure that you only use lavender that has been produced for culinary usage (often found in bulk form at health food stores). If it isn't sold in a food store, don't use it (such as that in craft stores).
-A little goes a long way. Too much and your mouth will taste like it was washed out with soap.
Now for some of the items I have done with it:
Lavender ice cream (Lavender & Honey even better!) is a common use. Infuse the cream with the lavender buds by bringing it to a simmer and then take off the heat and cover, letting sit for about 30 minutes.
Lavender orange sorbet (infuse lavender buds into the orange juice).
I've also used lavender and thyme in an herb past rub for roasted lamb.
"English Garden Madeleines" using dried lavender and rosewater in the madeleine batter.
I did a presentation on culinary uses of lavender a dozen years ago and don't quite recall what else I did with it but should be able to pull out the recipes I mentioned above.
If you'd like the recipes, email me at: darin@chefdarin.com and I'll forward them to you.
Temperature is certainly important. If you start out with a hard candy straight from the pot you're gonna be largely out of luck regardless.
But really, the signature taffy texture comes from the continual pulling, folding, pulling that happens after you remove it from the heat. Pulling taffy works lots of air into it and stretches out the strands of sugar crystals into thinner, chewier shapes. So be sure you really work that taffy once you take it off the heat (and before cutting it).
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This is going to sound odd, but taffy is actually a great ingredient in sweeter coffee drinks like mochas. It melts into the drink adding sugar and flavor. I'm a fan of banana for this purpose.
In a similar vein, you could also use the taffy as a chip in cookies. Chop it up and use it wherever you think banana flavor would taste good. I could imagine the banana taffy going well in with macadamia nuts. You might want to consider the taffy as a substitute for butterscotch or white chocolate chips in recipes requiring them.