Arrange the peaches, cut side down, in a spiral pattern around the bottom of the tin. Set aside.
Bake for 45 to 50 minutes or until golden brown and firm to the touch, covering with foil after 30 minutes if the cake begins to brown too much.
Combine sugar, eggs, yoghurt, melted butter and vanilla in a large bowl and beat until smooth and well mixed. Sift over the flour, baking powder and salt, and fold in gently.
Spoon the mixture into the tin, over the peaches, and smooth the top.
Let the cake cool in the tin for about 15 minutes, then run a knife around the sides and remove the rim of the cake tin. Invert onto a serving plate. If desired, warm the apricot jam and brush over the peaches. Leave to cool completely before slicing and serving.
Preheat the oven to 180 C / Gas 4. Grease a 23cm round springform cake tin and line the bottom with a circle of baking parchment.
For an impressive finishing touch, skip the apricot jam and instead dust the top of the cooled cake with about 2 tablespoons of caster sugar. Using a creme brulee torch, caramelise the sugar on top of the peaches till a deep golden brown.