Pre-heat the oven to 200° C.
Roll the pastry out to 1½cm thickness on a lightly floured surface. Use it to line a 7inch springform fluted tart tin. Prick the base and line with greaseproof paper and baking beans.
Blind bake for 15 minutes until the edges just start to colour. Remove from the oven and discard the greaseproof paper and baking beans. Return to the oven to brown the base for minutes.
Remove after 5 minutes and brush the base with the beaten egg. Return to the oven for 1-2 to let the egg set and form a seal, then remove and transfer to a wire rack to cool.
Spoon the apricot jam into the pastry case, then smooth using the back of a hot, wet tablespoon or palette knife. Arrange the peach slices around the outer border of the tart in a circle, leaving a space in the centre of the tart.
Reassemble a peach half using the slices of peach, then place it in the centre of the tart. Dot the peaches with the butter, then sprinkle over the sugar.
Return to the oven for 10 minutes until the peaches are lightly coloured and the jam filling is hot. Serve hot.