yes, you are right it is more spongy because it is made with white yogurt as a healthy addition. If you are looking for more of a traditional recipe I found this one (on easterneuropeanfood.com). Not sure about the cream of Tartar (that’s instead of the baking powder? or the orange liquer additon; I would just substitute with some lemon grind):
Ingredients:

1/2 cup (1 stick) butter, softened
1/2 cup sugar
3 large eggs divided, at room temperature
1 tablespoon Grand Marnier or other orange liqueur (optional)
1 teaspoon orange zest
1/2 teaspoon salt
Pinch of cream of tartar
1 cup all-purpose flour
2 cups fresh blueberries, washed and stemmed
Confectioners’ sugar
Blueberry Sauce (optional but see below)

Preparation:

Place rack in center of oven and heat to 350 degrees. Butter or lightly coat with cooking spray a 9-inch-by-9-inch baking pan. In a medium bowl, cream together butter, sugar and yolks until light and fluffy. Add liqueur, if using, orange zest and salt, mixing well.

In a clean medium bowl, beat egg whites with cream of tartar until stiff. Alternately fold in egg whites and flour into butter-egg mixture.

Turn batter into prepared pan and scatter blueberries evenly over top. Press down into batter with a spatula. Bake 30 to 40 minutes or until toothpick inserted near center comes out clean. Cut into 6 equal pieces. Serve warm or cold dusted with confectioners’ sugar and blueberry sauce, if desired.

greets from México.
Estephanie

Sorry, I forgot to put the eggs into the step 1. You basically add them together with everything else: milk, yogurt,sugar, butter, and EGGS.
It makes it really easy that way; you combine all of the ingredients, slowly mix in the flour, pour in to the baking dish, drop in the fruit, bake and eat!
Hope your Czech husband loves it! Let us know..