Mix the cheese, mayonnaise, and onion together.
Stir in the nuts until well incorporated.
Season with cayenne and black pepper to taste.
Pack into a 2-cup ring mold or other mold; a bowl would work as well.
Cover with plastic wrap and chill overnight until firm.
Unmold onto a serving plate. If needed, dip the mold briefly in hot water and run a knife around the edges.
Decorate with whole pecan halves, if desired.
Keep refrigerated until just before serving.
Serve with strawberry preserves or plain, with crackers. If using a ring mold, Rosalynn suggested placing the preserves in the center of the ring.