A very low-bake double-crust pie of sweetened white pastry filled with
whimberries (wimberries, bilberry, whortleberry or winberry) often with apple. Top crust splashed with threads of water-icing.

Wimberry pie made in Glossop
Image: Chrissi Nerantzi https://www.flickr.com/photos/chrissinerantzi/
So-called from the propensity of whimberry to stain the diner's mouth blue.