Note: Thanks to reader feedback, as of as of 6/19/12 this recipe has been corrected/revised to use 4 cups of nuts (16 ounces), rather than the 2 cups previously listed. Thanks, readers - and sorry for the mistake.
1) Preheat oven to 250°F. Line a baking sheet with parchment or foil for easy cleanup.
2) Combine the melted butter, sugar, and apple pie spice in a large bowl. Stir until smooth. Add pecan halves. Stir and toss until the nuts are well coated.
3) Pour nuts and any leftover butter/sugar onto a lined baking sheet and place in the oven for 10 minutes. Remove from the oven and sprinkle with half of the vanilla powder. Stir well and return to the oven for an additional 10 minutes.
4) Remove nuts from the oven for a second time. Add the remaining vanilla powder and stir well again. If any butter/sugar liquid remains, return the pan to the oven briefly until most of the mixture has cooked onto the nuts.
5) Set the nuts aside on the pan to cool. Serve slightly warm, or at room temperature. Sprinkle with additional vanilla powder and/or salt if desired. Store at room temperture in an airtight container for up to one month. These sweet nuts make an excellent stocking stuffer or hostess gift.