Butter tart is a humble food that achieved iconic status in early 20th-century Canada. The filling is traditionally made with a combination of walnuts, eggs, brown sugar, butter, and white vinegar, and it's then placed into small, flaky, deep or shallow tart shells before baking.
Early versions of the recipe, dating back to 1915, suggest that currants and raisins should also be included in the mixture. There are lots of theories about the origin of the tart – some say that it is related to pecan pie, which was brought to the country by American slaves, some say it evolved from Quebec's sugar pie, while others say it's linked to Border Tarts from southern Scotland.