You will need to use a hot or very hot oven, usually 220C. If the oven is not hot enough, the butter will run out of the pastry layers before it is absorbed by the starch. If the butter runs at this oven setting, check the temperature of your oven or use a higher setting. If you are using bought pastry, check the oven temperature
on the pack and be sure you preheat the oven for long enough; at least 20 minutes.
Some recipes advise reducing the oven temperature after the initial cooking. This allows time for the filling of the dish to cook sufficiently while preventing the pastry from cooking too quickly.
** Cooking Temperatures