Generously butter a 8-in sandwich tin and
sprinkle the sugar over it. Peel, core and quarter the apples and
arrange around the tin, just overlapping, in concentric rings. Dot on
the rest of the butter and put on to a hotplate or gas ring. Watch over
it very carefully to check that the sugar caramelizes evenly without
burning; if necessary, move the tin from side to side of the ring to
obtain even browning. Leave to cool.
Roll out the puff pastry and cut it into a
circle to fit the sandwich tin. Cover the apples with this pastry, glaze
with the beaten egg yolk and bake in a hot oven 220C, 425F, Gas 7 for
20-25 minutes. Turn out and serve upside down with the apples on top.
