In a mixing bowl, rub the butter into the flour until the mixture resembles fine breadcrumbs. Mix in the egg, salt and lemon juice and knead until a dough forms. Wrap in cling film and chill in the fridge for 1 hour.
Preheat the oven to 190 C / Gas 5. Grease a quiche dish.
For the filling:
Meanwhile, in a bowl combine the milk, cream and eggs and beat well. Add the feta followed by the vegetables and the salmon. Season.
Remove the pastry from the fridge and roll out on a floured surface. Transfer to the prepared quiche dish and press gently into the base and sides to line. Pour in the filling.
Bake for 1 hour until the filling is firm and the pastry is golden brown.