Blueberry-Orange Upside-Down Cake

Place oven rack in lowest position and heat oven to 375 degrees F. Using softened butter, grease two 6-cup nonstick muffin pans or one 12-cup pan (smaller pans will be easier to flip over later). Dust each cup with granulated sugar; tap out excess sugar. Topping: Melt butter in a small saucepan. Add brown sugar and cook, stirring, over medium heat until sugar dissolves and mixture looks creamy and smooth, 2 to 3 minutes. Remove from heat and spoon mixture into bottoms of prepared muffin cups, about 1 tablespoon per cup. Arrange blueberries in a single layer on top of sugar mixture in each cup. Set aside. Cake batter: Whisk flour, baking powder, cinnamon, and baking soda in a small bowl. In the large bowl of a stand mixer (or using a hand mixer), beat butter and sugar until creamy. Beat in orange zest. Beat in eggs until combined. With mixer on low, alternately beat in flour mixture and buttermilk mixture until batter is thick and smooth. Fill muffin cups. Tap pans on counter to settle batter. Bake 16 to 18 minutes or until a toothpick inserted in the center of a cake comes out clean. Let cakes cool in pans on a wire rack for 5 minutes. Invert a large plate or platter over the top of each muffin pan, and flip pan over to release cakes. Serve warm or at room temperature. Top cakes with an additional cup blueberries, and dust confectioners' sugar on top.