Here's a recipe from Lyle's himself.
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. 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.
To those in the UK, the familiar taste of golden syrup usually makes tart quite appealing. Golden syrup frequently tops porridge in place of brown sugar or maple syrup, and is thus reminiscent of childhood fare.