Every July and August, Finns head into the forest with buckets and berry pickers, and the bilberries they bring home, small, wild and stained deep blue right through, become mustikkapiirakka. Thanks to everyman's right, the old custom that lets anyone pick berries in the forests, the main ingredient is famously free, and the season is short enough that nobody wastes it. The most popular version has a soft, cake like crust pressed into the tin by hand, a thick layer of berries and a sour cream custard that sets around them in the oven.

It is the pie of summer cottages and coffee tables, eaten warm with vanilla sauce or ice cream. Frozen wild blueberries make an excellent year round substitute, so it is just as welcome in October, when the season's final races are run and summer needs remembering.

The crust

Ingredients

• 1/2 cup (115 g) unsalted butter
• 1/3 cup plus 1 tablespoon (85 g) sugar
• 1 large egg
• 1 1/2 cups (180 g) all purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon ground cardamom

Method

1. Heat the oven to 400°F (200°C) with a rack in the middle. Rub the pie dish with a little butter.
2. Beat the butter and sugar together in a bowl with the wooden spoon or mixer for 2 minutes. Beat in the egg.
3. Mix the flour, baking powder and cardamom, add them to the bowl and stir just until a soft dough forms.
4. Put the dough in the dish and press it out with lightly floured fingers over the bottom and about 1 1/4 inches (3 cm) up the sides, keeping it as even as you can.

The berry and sour cream filling

Ingredients

• 2 cups (300 g) bilberries or wild blueberries
• 1 cup (240 ml) full fat sour cream
• 1 large egg
• 1/4 cup (50 g) sugar
• 1 teaspoon pure vanilla extract

Method

1. Scatter the berries evenly over the bottom of the crust.
2. In the second bowl, whisk the sour cream, egg, sugar and vanilla until smooth. Pour it slowly and evenly over the berries.
3. Bake for 30 to 35 minutes.
4. Set the pie on the rack and leave it for at least 30 minutes before cutting.

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