Treacle pie is another name for treacle tart, a pastry-crusted, syrupy sweet treat mixed with breadcrumbs and lightened with lemon zest. Pie gives us a traditional recipe.
'treacle' on Serious Eats
If you've been reading about the Treacle Tart throughout the Harry Potter series, this is your chance to finally taste the real thing. Adapted from The Unofficial Harry Potter Cookbook by Dinah Buchholz, imagine it as a pecan pie minus the pecans. A sweet, double crusted pie filled with a dark, sticky sweet filling of golden syrup, breadcrumbs, and lemon juice and zest.