(NYTIMES) - You could be forgiven if you have never eaten a butter tart. There is no flashy frosting or elaborate lattice to entice you.

It is easy to pass by.

But Canadians will tell you that these diminutive treats hold an expanse of flavour and textures: flaky pastry, caramelised crust and a bracingly sweet filling.

The butter tart is celebrated in its homeland, where the preference for runny or firm fillings, plain or with raisins, is a matter of passionate national debate.

Ontario, where most scholars believe the butter tart was born, celebrates it with two duelling tourism trails (Kawarthas Northumberland Butter Tart Tour and Butter Tarts and Buggies) and festivals galore, including Ontario's Best Butter Tart Festival in Midland and a new one that will have its debut in March in Bowmanville, east of Toronto.

"Good butter tarts, they seem like a modest dessert," said Michael DeForge, a creator of TartQuest, an Instagram feed of butter tart reviews.

"They're supposed to pack a lot of punch. But on the outside, they're supposed to just seem plain and unassuming."

Modern Canadian culinary culture celebrates seasonality, native ingredients and provincial pride. Like poutine and Nanaimo bars, two other national favourites, butter tarts buck the norm.

They are a humble treat, made with ordinary ingredients, and spectacularly delicious.

"If you look at the ingredients, it's really what you have in your pantry when you have nothing else," said Liz Driver, author of Culinary Landmarks: A Bibliography Of Canadian Cookbooks, 1825-1949.

At its most basic, the butter tart is a pastry filled with brown sugar, butter and egg. Oven alchemy transforms those simple ingredients.

Inventive cooks have gone further with chocolate chips, coconut, nuts and other add-ins.

Unlike the Nanaimo bar - a mid-century British Columbian creation made with processed ingredients such as custard powder and graham crackers - the butter tart goes back at least to the 19th century.

Mary F. Williamson, a retired fine arts librarian at York University in Toronto, traced the earliest mention to 1900 and the Royal Victoria Cook Book, published to raise money for the Royal Victoria Hospital in Barrie, Ontario.

Margaret MacLeod's recipe for "Filling for Tarts" (like some of the other community cookbook contributors, she was identified by her husband's name, Mrs Malcolm MacLeod) called for one cup of sugar, a half-cup butter, two eggs and a cup of currants.

There are as many theories about the origins of the tart as there are variations.

The brown sugar pie, the Scottish border tart, Bakewell tarts and the Quebec sugar pie - each has been named a predecessor to the Canadian tart.

"Each of those things is its very own particular thing, very similar to each other, but they're not all the same," Driver said.

The very first butter tart recipe may never be found because, until recently, cookbooks were not seen as items worth preserving.

"Most of these things were developed by housewives and it wasn't deemed important," said Lenore Newman, author of Speaking in Cod Tongues: A Canadian Culinary Journey. "Now that we're actually interested in it, we go back and we find there are a lot of holes in this knowledge. I think we can safely say they're Canadian and that they're definitely still popular."

By the 1910s, the butter tart was all the rage in the farming regions of Ontario. Three recipes for tart filling and six recipes for butter tarts appear in Canadian Farm Cook Book of 1911.

"Junia," a columnist for The Farmer's Advocate, shared reader recipes in early 1913 to answer a question from N.W. of Ontario who longed for a butter tart recipe - "the crust and all, as I am a new beginner".

Readers responded with tart recipes plain and with currants, proof perhaps that the filling debate over plain or dried fruit is more than a century old.

Butter tart recipes, and variations such as butter tart ice cream, regularly appear in magazines such as Canadian Living.

Elizabeth Baird, who was food editor of the magazine from 1987 to 2009, was a student at the University of Toronto when she realised the power of their appeal.

"I worked in a summer lodge where there were a lot of American visitors and we could wow them every time with butter tarts with vanilla ice cream," Baird said. "I think that was the first time I realised they were unique to Canada."

Why, then, have the tarts never made significant waves south of the border? It could be that Canadians do not want to let the world - or just their louder neighbors - in on their sweetest secret.

"You have so many things of your own," Driver said with a laugh. "You don't need a Canadian butter tart."

Butter Tarts

INGREDIENTS
For the pastry
1½ cups all-purpose flour, more for dusting
Pinch of fine sea salt
½ cup cold unsalted butter or lard, cubed
¼ cup ice water
1 large egg yolk
1 tsp white vinegar

For the filling
¼ cup raisins (optional)
1 cup packed brown sugar, light or dark (see Note)
½ tsp fine sea salt
¼ cup unsalted butter, softened
1 tsp vanilla extract
1 large egg

METHOD
1. Make the pastry: In a large mixing bowl, combine flour and salt. Using a pastry blender or your fingertips, rub butter or lard into flour until mixture is in pea-size pieces.
2. In a small bowl, mix water, egg yolk and vinegar until well combined. Add liquid to the flour mixture, using a fork to combine. Add 1 Tbs more water if it looks dry.
3. Knead dough several times by hand to bring it together and shape into a flat square. Wrap with plastic and refrigerate for at least 30 minutes.
4. Once chilled, roll out the dough into a 40cm by 30cm rectangle about 3mm to 6mm thick. Flour the work surface and rolling pin as you work with the dough.
5. Use a circular 10cm cookie cutter to cut 12 pieces. Reroll dough if needed to cut more circles, but try to cut as many pieces on the first pass. With your fingertips, press each circle into the cup of a standard muffin tin, so that the edge of the dough is flush with the pan. Refrigerate while you make the filling.
6. In a bowl, cover raisins with hot tap water to plump. Heat oven to 220 deg C).
7. Make the filling: In a bowl, mix brown sugar and salt, and then beat the butter into the sugar by hand until smooth. Add vanilla and egg and mix until combined. Do not use an electric mixer; it will add too much air to the filling.
8. Drain the raisins and place seven or eight raisins in each chilled tart shell.
9. Divide the filling evenly among the tart shells, filling each one about halfway. Place muffin tin on a baking sheet. Bake 13 to 15 minutes for a runnier
tart and 17 to 19 minutes for a firmer one.
10. A few minutes after removing the tarts from the oven, run a knife or offset spatula around the edge of each tart to loosen. Let cool completely in the tin. To remove, run a butter knife or offset spatula around and under each tart to pop it out of the tin.

Makes 12

Butter Tart Squares

INGREDIENTS
For the crust
1¼ cup all-purpose flour
¼ cup packed brown sugar, light or dark
Pinch of fine sea salt
½ cup cold unsalted butter, cubed

For the filling
⅓ cup/76 grams unsalted butter, softened
2 Tbs heavy cream
1 tsp vanilla extract
½ cup raisins, roughly chopped (optional)
1 cup packed brown sugar, light or dark
1 large egg, beaten
1 Tbs all-purpose flour

METHOD
1. Heat oven to 180 deg C). Make the crust: In a bowl, combine flour, brown sugar and salt. Using a pastry blender or your fingers, cut in butter until well combined and crumbly. It will be dry and sandy. Press flour mixture evenly into a 23cm square pan and bake for 15 minutes.
2. As the crust bakes, make the filling: In a bowl, mix butter, cream, vanilla, raisins (if using), brown sugar, egg and flour until combined. Spread to edges over partly baked crust.
3. Return to oven and bake 14 to 20 minutes more or until golden brown (squares made with dark brown sugar will be a deeper shade of amber). A few minutes after removing it from the oven, run a knife or offset spatula around the edges to loosen any sugar that is stuck to the pan. Let pan cool to room temperature, then chill in a refrigerator. Once cold, use a sharp knife to slice into squares, approximately 4.5cm

Makes 25 squares