This easy recipe for Polish lemon blueberry Bundt cake, or cytryny-borowkowy ciasto bundt (blueberries are also known as czarna jagoda), uses a packaged lemon cake mix, fresh berries, sour cream, and eggs. Packaged cake mixes have reached even the remotest villages in Poland these days.
Heat oven to 350 F. In a medium bowl, gently toss blueberries and zest, if using, with flour and set aside.
In a large bowl, combine cake mix and sour cream. Add eggs one at a time, beating at low speed after each addition. Continue to beat at medium speed 2 minutes. Fold in blueberries and zest.
Coat a 10-inch Bundt pan with cooking spray. Transfer batter to pan and bake 35 to 40 minutes or until toothpick tests clean. Cool in pan on a wire rack for 15 minutes before inverting. Cool completely. Dust with confectioners' sugar or pour on lemon glaze. Serve with blueberry sauce, if desired.