1
: Line 9-inch (23 cm) pie dish with foil and baking sheet with waxed paper; set aside.
2
: Combine sugar, evaporated milk and butter in large saucepan; bring to rolling boil over medium heat, stirring constantly. Boil 4 to 5 minutes or until mixture starts to thicken. Reduce heat to low. Stir in white chocolate until completely melted; remove from heat. Stir in marshmallows until melted; stir in walnuts (if desired). Pour into prepared pan.
3
: Working quickly, pour semisweet chocolate into small plastic bag; snip small hole in corner. Squeeze dark chocolate in concentric circles on top. Beginning at centre, pull tip of knife through fudge and circles to form cobweb pattern.
4
: Drizzle remaining semisweet chocolate onto prepared baking sheet to form spiders with wriggly legs. Chill fudge and spiders in refrigerator. To serve, hold foil to lift fudge from pan; peel off foil. Place fudge on plate; garnish with spiders.