How to get the crunch without burned nuts?

Pecans roast really quickly. I think I’d try layering in the topping and the pecans, and returning the pie to the 325 degree oven (with foil on the crust) for 10 minutes. The pecans will likely be lightly toasted and not burned. You can always finish with a quick carefully watched blast of the broiler if you want them darker.

Or, cook the pie and the topping separately. Watch the topping so it doesn't burn, remove from oven. Combine with pie and serve.

Or, cook the pie and the topping separately. Watch the topping so it doesn't burn, remove from oven. Combine with pie and serve.

It sounds like your broiler might be run on the hot side. Are you placing the pan 6" below the heating element? Are you leaving the door ajar? I'm guessing you are. Perhaps try lowering the rack an inch or two. Or maybe you could put the topping on, cover the whole thing with foil, and broil for a few minutes to get the topping hot without burning the nuts, and only then remove the foil and broil, exposed, for a few minutes, watching it like a hawk all the while. ;o)