1 1/2 cups granulated sugar
1/2 cup packed dark brown sugar
1 cup dark rum
2 cups walnut halves
Line large baking sheet with aluminum foil.
Combine granulated sugar, brown sugar and rum in medium size heavy saucepan. Bring to boiling over medium-high heat. Continue cooking until temperature registers 275 degrees F on a candy thermometer, 15 to 25 minutes (soft crack state - mixture forms pliable strands when drizzled from a metal spoon into a bowl of cold water).
Stir in walnuts. Quickly pour out onto prepared baking sheet, spreading out with metal spatula as you pour. Let cool completely.
Break into 2-inch pieces. Store in airtight container in cool, dry place for up to 2 months.