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.