2) Combine the sugar, golden syrup, allspice and water in a medium saucepan. Stir over medium heat until the sugar dissolves. Increase the heat to high, and continue to cook, without stirring, until the mixture becomes an amber caramel, about 5 mins. Pour the caramel into the prepared tin and set aside to cool.
3) Halve and pit the peaches, but leave their skins on. Cut each half into 3 wedges. Arrange the wedges in concentric circles in the tin. Set aside while you make the cake batter.
For the cake:
1) Whisk the flour, cornmeal, baking powder, bicarbonate of soda and salt in a medium bowl.
2) Slowly mix the butter and sugar in a large bowl with a hand-held electric mixer. Increase the speed to high, and continue beating until the butter is light and fluffy, about 5 mins. Add the eggs 1 at time, waiting for each to be fully incorporated before adding the next.
3) While mixing at a low speed, add the dry ingredients in 3 additions, alternating with the sour cream in 2 additions, beginning and ending with the flour. Increase the speed to medium and mix briefly to make a smooth batter. Pour the batter over the peaches and smooth over.
4) Bake the cake until golden brown and a cocktail stick inserted in the centre comes out clean, about 40 to 45 mins. Cool the cake in the tin on a rack, about 20 mins.
5) Run a knife around the edge of the tin to release the cake. Carefully invert the cake onto a serving plate and remove the greaseproof paper. Serve warm or at room temperature with ice cream or whipped cream, if desired.