I used 10-inch round high-sided cast-iron skillet. You can also use a regular 8-inch or 9-inch round cake pan or a 9x3-inch springform pan.
Preheat oven to 350°F with rack in middle. Grease the sides and the bottom of the cast-iron pan with butter.
Sift flour, baking powder, baking soda, together into a medium bowl.
In a separate bowl, beat 2 oz of softened butter, sugar, and 2 eggs until very light in color and fluffy, 2-3 minutes on high speed.
Add vanilla and Greek yogurt and continue beating until very creamy and light in color, for about 1 more minute.
Keeping the mixer speed low, mix in the flour mix until combined. Do not overmix.
Transfer the cake batter to the cast-iron skillet. Top with sliced peaches, and scatter blueberries evenly on top in the spaces between the peach slices.
Bake uncovered until the cake turns golden, and the tester comes out clean in the center, about 45 minutes to 1 hour, depending on your oven. Midway through baking, I like to put some extra peach slices and extra blueberries on top of the cake for presentation purposes, and return the cake to baking.
When the cake is done baking, remove it from the oven and let it cool in a cast-iron skillet.