Preheat oven to 350°F. Line the base of an 8-inch round baking pan with parchment paper. Lightly grease the sides.
For the topping, toss peach wedges and blueberries with sugar in a bowl, then transfer to the base of your lined pan in an even layer.
For the cake batter, sift flour, baking powder, baking soda, cinnamon and salt into a medium bowl and whisk to blend evenly.
Beat butter with sugar and vanilla in a medium bowl using an electric hand mixer for 2 minutes on medium-high speed until pale and fluffy. Beat in egg until incorporated and then mix in honey. Mix in sour cream. Add half of the flour mixture and beat on low speed until just combined. Add the milk and beat until evenly blended. Add remaining flour and mix just until combined and batter is smooth. Scrape down the sides and bottom of the bowl as necessary while mixing.
Dollop batter over the fruit in the pan and spread it out evenly to the sides. Bake for 40-50 minutes until the top is evenly browned, it springs back when pressed gently and a wooden skewer inserted into the center comes out clean.
Transfer pan to a wire rack and let cool completely. It will sink slightly as it cools, leaving you with a flat cake perfect for inverting. Once cooled, invert cake onto a serving plate and peel off the parchment before serving.