Rub the butter into the flour until it resembles fine breadcrumbs. Stir in the oregano, salt and pepper.
Beat the egg with two tablespoons of cold water and mix into the flour: knead until it forms a soft and elastic dough. Wrap in clingfilm and chill for 30 minutes.
Use to line a a tart tin, prick the base with a fork and chill again for 15 minutes. Preheat oven to 200°C.
Line with foil or baking parchment, then fill with baking beans. Bake blind for about 10 - 12 minutes.
Remove the foil and baking beans and return the pastry case to the oven for a further 5 - 7 minutes to dry out completely. To prevent pastry from becoming soggy from the filling brush the blind-baked case with beaten white egg and bake again for 5 - 10 minutes until set and shiny.