Whisk the yolks, cornstarch, and the 40 grams sugar in a medium bowl; the mixture will be very thick, but try to whisk enough to remove most of the lumps.
Put the 75 grams sugar in a medium saucepan
and cook over medium heat until dark brown; don't worry if it crystallizes a bit. Turn the heat to low and whisk in the maple syrup, then whisk in the whisky, turn up the heat, and let simmer
for 1 to 2 minutes to boil off the alcohol
Whisk the milk
and vanilla bean scrapings into the caramel
mixture and bring to simmer. Slowly whisk about half of the hot mixture into the yolks, then whisk that mixture back into the pot, bring to a boil, whisking, and cook, still whisking, until thickened. Remove from the heat and whisk in the butter, salt and maple extract
. Pour into a shallow dish, press plastic wrap
onto the surface, and chill until set and very cold, about 4 hours.
Beat the cold pastry cream in a standing mixer until smooth. When ready to use, whip the cream until it is very stiff, then beat into the pastry cream. Chill until ready to use.