Preheat the oven to 200 °C and grease a rectangular loose-bottomed pie tin with non-stick spray.
Roll out the pastry to a thickness of 3 mm.
Line the pie tin with the pastry, allowing the edges to overlap the rim of the tin.
Brush with a little of the whisked egg and sprinkle with sesame seeds.
Line the shell with baking paper and fill it with dried beans or rice.
Bake for 15 minutes or until pale brown.
Remove from the oven and remove the paper and beans.
Reduce the oven temperature to 180°C.
Melt the butter and stir-fry the celery and onion until soft.
Spoon into the pie shell, spreading evenly.
Crumble the blue cheese on top.
Beat together the remaining egg and sour cream, season with salt and pepper and pour over the filling.
Bake for 30 to 40 minutes or until firm.
Remove from the oven, cool for 10 minutes in the tin and serve hot or cold with a green salad.
Note:You can use phyllo pastry instead of shortcrust pastry for the shell. Use about six sheets and spray each with non-stick spray. Line the pie tin the phyllo layers (no blind-baking required).