Place very clean glass or metal bowl and metal whisk in freezer just until cold, about 5 minutes.
When everything is cold, place cream in bowl and begin to whisk until it froths up and starts to thicken, about 1 minute. Whisk vigorously until soft peaks form (the cream will hold a point when the whisk is lifted but will fall back into the bowl almost immediately), about 1 minute.
Add the liqueur and whisk until stiff peaks just form (the cream stays put on the whisk when it is lifted from the bowl), about 1 minute. Store covered in refrigerator until ready to use.