Tracey,
Well, I'm not sure what they make for county fairs in North Dakota, but from your description, it sounds like the kuchens they bake in Alsace, France (that's German-influenced and a lot of the recipes have German names). The typical Alsacian kuchen calls for Italian prune-plums, but I see no reason why it can't be made with blueberries instead. It's a kind of custard filling in a pie shell, with fruit added.

Alsatian Zwetschgenkuchen
1 10" tartCrust:
1/4 pound butter
1/4 cup sugar
dash salt
2 eggs yolks
grated peel of 1/2 lemon
1 tablespoon lemon juice
1-1/2 cups flour
2 tablespoons seedless raspberry jam

Filling:
2 pounds Italian prune plums or apricots, halved and pitted
2 eggs
1/4 cup superfine sugar
3/4 cup heavy cream
grated peel of 1/2 lemon
1/4 teaspoon vanilla extract

Preheat oven to 450 degrees.
In a food processor, combine butter, sugar, salt, egg yolks, lemon peel, and lemon juice. Pulse until blended. Slowly add the flour and process just until well blended.

Turn out dough and press into the bottom and sides of a loose-bottom tart pan. Flute the sides.
Bake 10 minutes.

Brush the inside of the pastry shell with a thin layer of jam. Bake 5 minutes longer. Remove from the oven and lower oven temperature to 350 degrees.

Arrange plums or apricots over tart crust, cut side down.

Beat eggs and sugar together, then beat in cream, lemon peel, vanilla, and any leftover juice from the fruit. Pour custard mixture over the fruit.

Bake 30-35 minutes, until a knife inserted in teh center of the custard comes out clean. Serve warm or at room temperature.