In a stand mixer fitted with the whip attachment, whip the cream and sugar on medium speed until stiff, about 5 minutes. Transfer the whipped cream to a bowl.
Transfer the custard cream to the mixer bowl and whip briefly to smooth out the cream and ensure there are no lumps. Pour in the Frangelico, then slowly add the whipped cream. Stop and scrape the sides and bottom with a rubber spatula, then continue to whip until smooth and airy.
Transfer the filling to a pastry bag fitted with the #5 plain tip. Use your pinkie to hollow out the puffs from the bottom and pipe cream into the puffs through the hole. Pipe the cream puffs full of cream.