First make the topping. Heat oven to 180C/160C fan/gas 4. Grease a 20 x 30cm baking or roasting tin and line with baking parchment. Sprinkle with the sugar-flour mix. Push a raspberry or cherry into the cavity of each peach half, then place the peaches, cut-side down, in the tin.
To make the sponge batter, beat the butter, flour, sugar, baking powder, eggs, yogurt and vanilla in a large bowl with an electric whisk until lump-free. Spoon the mix into the tin, over and around the peaches, then bake for 50 mins-1 hr until golden and risen and a skewer poked in comes out clean.
Cool briefly, then carefully run a cutlery knife around the edges to release any stuck bits. Turn the cake out onto a board and cut into squares. Delicious eaten warm with ice cream.