Heat milk and cinnamon stick to boiling in medium saucepan over medium-high heat. Add crème caramel mix; heat to boiling again with continuous stirring, ensuring powder has fully dissolved.
Add vanilla; remove cinnamon stick.
Pour mixture carefully into 4 (150ml capacity) heatproof molds or serving cups. Cool slightly, then refrigerate about 2 hours or until fully set.
Brush oil in a shallow baking pan. Place sugar in large skillet. Place skillet over medium-high heat to melt sugar, swirling skillet occasionally to ensure it melts evenly – but do not stir, or it will crystallize. When sugar starts to turn golden, add walnuts. Stir briefly, then carefully pour onto oiled pan. Cool 10 minutes, then break into small pieces.
Beat whipping cream mix and cold milk in medium bowl as directed on package.
Gently run knife around sides of mold, and turn out onto plates to serve. Serve with brittle and whipped cream.