"Toast" is a unique movie. I would say it is a memory play. Like memory, it's patchy at times, with not all things explained. Bits and pieces of scenery; dialogue here and there; some things left out and some things exaggerated.
Did his mother really attempt cooking by putting unopened tins of food in a pan of water? Did the family really eat only toast at mealtime? The tone of most of the film is a sort of fairy tale or heightened realism. It's almost like someone's dream of days gone by, plucked from their memory and shown onto a flickering movie screen.
Did his father's inamorata really have a mania for cleaning and chain smoking? What was her situation with her husband? Was he alive or dead? She at times seems a lovelorn hausfrau and at times the witch from Hansel and Gretel, fattening his father up for the kill. There's very little about her that seems realistic, but perhaps that is deliberate.
Did Nigel's father really sneer at him that often? Did his mother do little else besides reach for an inhaler? What was her health problem? If his father told Nigel to wait until morning to open his gifts, why didn't he -- how did Nigel know his mother had died? Why isn't his mother's death shown in the film?
There are some strange choices made but the overall impression is like a watercolor. View it too closely and it lacks cohesion. View it as a whole and there is a definite life story to be seen.
The old saying goes "food is love," yet in this film, the mother who loves Nigel and who he loves can barely make toast. The woman who later wins his father's heart "by way of his stomach" can cook and bake like no other, yet she and Nigel barely tolerate one another. Nigel resolves early on to never like his father's friend/cleaner/new love, and he never budges in that.
Mrs. Potter, for her part, while continuing to cook, bake, clean, and keep house with the power of ten women and world class chefs, never seems to see Nigel as he is. It's a pity they compete over cooking rather than bond over it, but neither can truly empathize with the other.
So in this film at least, food is not love; Mrs. Potter's overweening culinary attentions to Nigel's father seemingly contribute to his death, from heart disease. She knows the difference because at the end she promises Nigel she will only cook healthy foods from then on. So the film implies throughout that she deliberately uses food as a weapon: undermining and competing with Nigel for his place in his father's heart, and damaging his father's heart by stuffing his father night and day with freshly made delights.
His mother, in sainted memory, really never "fed" Nigel in any real way other than, she was his mother and never sought to hurt him. Otherwise she is portrayed as sickly and ineffectual at taking care of her family.
Interesting because the one food his mother made, toast, is enough for Nigel to cling onto and take with him as the symbol of "food is love" as he built his own eventual culinary career.
There is a subplot which may make some viewers uncomfortable: boy Nigel peers at the young gardener changing in the shed. He later is kissed by a co worker. Nigel in that scene is 16 and his co worker at least in his twenties. All of this is presented as if natural but some may find overtones of abuse in those scenes.
There's pity to be had for "Mrs. Potter," the character played by Helena Bonham Carter: With all her talent, she lives in poverty and relies upon the kindness of men for her survival. The film unironically looks down on her because she "lives in a council house" and "is just a cleaner," but with her talent for cooking and baking, why did no one suggest she open her own restaurant? Or go to cooking school?
Nigel makes his escape in the end, to a fancy hotel kitchen in another city, but Mrs. Potter is stuck in the home she plotted for, alone, with a cake no one is there to eat.