According to the folks at wiki:
Treacle is any syrup made during the refining of sugar cane and is defined as "uncrystallized syrup produced in refining sugar". Treacle is used chiefly in cooking as a form of sweetener or condiment.
The most common forms of treacle are the pale syrup that is also known as golden syrup and the darker syrup that is usually referred to as dark treacle or black treacle. Dark treacle has a distinctively strong flavour, slightly bitter, and a richer colour than golden syrup, yet not as dark as molasses. Golden syrup is the main sweetener in the Treacle Tart.
In popular culture
In chapter 7 of Lewis Carroll's Alice's Adventures in Wonderland, the Dormouse tells a story of Elsie, Lacie and Tillie living at the bottom of a well, which confuses Alice, who interrupts to ask. "The Dormouse again took a minute or two to think about it, and then said, 'It was a treacle-well.'" When Alice remonstrated, she was stopped by the Mad Hatter's analogy: "You can draw water out of a water-well, so I should think you could draw treacle out of a treacle-well." Alice said very humbly, "I won't interrupt you again. I dare say there may be one." This is an allusion to the so-called "treacle well", the curative St. Margaret's Well at Binsey, Oxfordshire.
In Series 3 episode 6 of Jeeves and Wooster, Bertie Wooster, while trying to make off with an unsightly painting, attempts to use treacle and brown paper to muffle the sound of broken glass. He is foiled, however, by the treacle's stickiness.
Harry Potter also often eats treacle tart in the Harry Potter book series by J.K. Rowling. Treacle tart is also mentioned in Agatha Christie's murder mystery novel, 4:50 from Paddington , as young Alexander Eastley's favourite dessert
Hmmmm....all this interesting Treacle information. They even mention treacle in popular literature BUT they managed to miss the appearance of treacle tarts, frequently, in our dear Betty's books. A horrible oversight!!!
Yes, fellow Betty lovers, I am sure that you have noticed the frequent whipping up of a quick treacle tart or as is mentioned in A Small Slice of Summer, the eating of the tart because it's ....well dare we say it, cheap and filling....
Letitia wandered along the counter with her tray, looking for something cheap and nourishing. She had bought a dress on her last days off and her pocket was now so light that buying her meals had become a major exercise in basic arithmetic.
She chose soup, although it was a warm june day, a roll to go with it and a slab of treacle tart, because starch was filling and even though it was fattening too she was lucky enough not to have that problem, being possessed of a neat little figure which retained its slender curves whatever she ate. she paid for these dainties at the end of the counter and went to join her fellow staff nurse, Angela Collins, who cast a sympathetic eye at the contents of her tray, said fervently, "Thank God, it's only a week to pay-day," and addressed herself to her own, similar meal.
Now, dear Bettys. we ask..."What is a treacle tart?"
According to WiseGeek (I thought I would change up authorities to keep you on your toes):
Treacle tart is a popular dessert in the UK. It has become somewhat of a curiosity in other countries due to its frequent mention in the Harry Potter books. Treacle tart is in fact, Harry’s favorite dessert.
For most anyone not British, great misunderstanding exists about treacle tart. Many assume that it is made with molasses, which is often called treacle in the UK. Actually treacle tart is made with golden syrup, a by-product of sugar making, like molasses, but more similar in taste and texture to honey. Golden syrup may also be referred to as treacle in the UK.
One may find golden syrup in the US in international food stores, and it can be purchased on the Internet so one can make the perfect treacle tart. If one cannot obtain golden syrup, honey is a close alternative ingredient.
Most treacle tarts begin with a very rich shortbread pastry as a base, usually containing butter, flour and an egg yolk added so that the pastry crumbs adhere to each other. The golden syrup is combined with breadcrumbs, lemon juice, and occasionally spices like ginger to form the filling of treacle tart. The tart is then topped with several strips of the pastry to give it a rich, crispy finish.
The treacle tart bakes for about 45 minutes, and temperatures may vary according to recipes. A treacle tart may be baked in small tins for individual tarts, or it may be baked in a larger pie tin to serve in slices.
Treacle tart has a consistency similar to pecan pie, though it usually does not contain eggs in the filling and is less gelatinous. It is slightly stickier. It can be served hot, warm, or cold, and may be garnished with whipped cream, or ice cream. It is a very sweet dish, and those unaccustomed to such sweetness may find it overly sweet.