To make the pastry first you slice butter into small chunks and
rub it into flour with your fingers until it resembles coarse breadcrumbs.
Add egg yolk and sugar and push it all together until it forms soft
dough - if it is too crumbly you might have to add some cold water
(tablespoon or so). If you have food processor you can mix it all
there but you lost all the fun. When the dough is ready, wrap it
into clingfilm and put to fridge to rest for about 30 mins.
Meanwhile prepare the plums.. Halve and stone the plums. You need
a heavy, solid bottomed metal pie dish or baking tin for this -
put it over a low heat and let butter and sugar melt until they
form a rich, honey-hued caramel - you have to be careful with this
as this mixture is likely to burn very easily so stir and keep an
eye on it to prevent that from happening.
When you have caramel, turn off the heat and push the fruit, cut
side up, into it. Roll the pastry out and place it over the fruit,
patching any holes as you go. Tuck the edges between fruit and the
tin and place the cake in the oven (190°C) where you should
leave it till the pastry is golden brown and caramel and fruit juices
are bubbling over the edge (beautiful sight). That will take 30
- 45 minutes. When it is ready, leave it outside to cool and then
turn it out.