Beat butter and cheese until blended. In another bowl, whisk flour, salt and cayenne; gradually beat into cheese mixture. Stir in Rice Krispies. If necessary, turn onto a lightly floured surface and knead 4-6 times, forming a stiff dough.
Divide dough in half; shape each into a 7-in.-long roll. Wrap and refrigerate 1 hour or overnight.
Preheat oven to 350°. Unwrap and cut dough crosswise into 1/4-in. slices. Place 1 in. apart on parchment-lined baking sheets. If desired, top each slice with a pecan half. Bake until edges are golden brown, 14-16 minutes. Remove from pans to wire racks to cool.
To Make Ahead: Dough can be made 2 days in advance. Freeze option: Freeze wrapped logs in an airtight container. To use, unwrap frozen logs and cut into slices. Bake as directed.