In a large bowl, mix the flour and salt. Create a well in the center and add the egg, oil, and warm water.

Mix the ingredients until a shaggy dough forms, then transfer to a floured surface and knead for about 5 minutes until smooth and elastic. Cover with a bowl and let rest for 20 minutes.

While the dough rests, toss the fresh blueberries gently with 1 tablespoon of sugar and the cornstarch in a small bowl.

Roll out the dough on a floured surface until it is about 1/8 inch thick. Use a round cutter or a glass to cut out circles approximately 3 inches in diameter.

Place a spoonful of the blueberry mixture into the center of each circle. Fold the dough over to create a half-moon shape and pinch the edges tightly to seal.

Bring a large pot of salted water to a boil. Drop the pierogi in carefully, cooking in batches to avoid overcrowding. Cook for 3-4 minutes; they are done when they float to the top and the dough looks tender.

While the pierogi cook, melt the butter in a skillet over medium heat. Add the breadcrumbs and 1 tablespoon of sugar, frying until golden brown and crispy.

In a small bowl, whisk the sour cream with the vanilla extract and remaining sugar.

Remove pierogi with a slotted spoon, top with the crispy breadcrumbs, and serve immediately with a dollop of the vanilla sour cream.