Combine sugar and butter in a 10-inch cast-iron skillet; cook over medium heat, stirring constantly, until sugar dissolves and becomes a golden syrup.
Remove from heat; stir in ground pecans. Working rapidly, pour mixture into a buttered 8-inch square pan. Mark top of warm candy into 1-inch squares, using a sharp knife. Cool completely before breaking into squares. Store in an airtight container.
Note: Ground walnuts or peanuts may be used in place of ground pecans.