Toffee: Melt the butter. Add the sugar, salt and vanilla and cook, stirring, until thick and bubbly. Pour onto parchment and let harden for ~15 min, then break into small pieces.
Cornflake crunch: Mix everything together, spread onto a lined tray and bake at 165C for 20 min until golden. Cool and break into pieces.
Cookies: Brown the butter until golden and nutty. Let cool slightly, then whisk with both sugars. Add the egg, egg yolk and vanilla.
Mix in the dry ingredients until just combined. Fold in the cornflake crunch, sesame and chopped toffee.
Scoop into 12 balls, top with extra toffee and chill for at least 1 1/2 hours.
Bake at 175C for 9-10 min. While warm, shape with a large glass. Top with extra cornflake crunch and toffee.