Nan and the mince

A teenage boyfriend visits me at Nan's house and is invited to stay for tea.  Her speciality mince with mashed potatoes and peas is on the menu.  Most of my Nan's cooking involves a 'secret' ingredient; this one is a packet of oxtail soup added to the greasy mince.  We sit down, Uncle silently reading the Oxford Mail, boyfriend being charming to Nan, Nan flirting like mad (she can't help herself) and me sulking because everyone is ignoring me. Uncle has a quizzical look on his face that morphs into disgust.  His rapid, somewhat desperate swallowing suggests his distress is food-related rather than something in the newspaper.  The mince tastes odd, not unpleasant, but not exactly right.  In fact in tastes of no oxtail known to man, woman or ox.
 'Muuuther, what have you done to the mince?' The cry of an anxious man who likes his food.
Boyfriend, having been at boarding school, will eat anything and empties his plate: 'Delicious, best mince I've ever had.'  It was at that moment that I realised our relationship probably wouldn't last.
Nan, delighted, offers him more.  Boyfriend, polite, greedy or possibly both accepts.  Nan disappears into the kitchen, only to signal wildly for me to join her.
'I think I've discovered why it tastes a bit odd,' she whispers dramatically, producing a packet of chocolate Instant Whip from behind her back.