Cook potato and cauliflower in a saucepan of boiling water for 10 minutes or until just tender. Drain. Return to the pan and using a fork, roughly mash mixture.
Heat oil in a frying pan over medium-high heat. Add onion. Cook, stirring for 3 minutes or until softened. Add garlic, celery, carrot and zucchini. Cook, stirring constantly, for 5 minutes or until carrot starts to turn golden. Add potato mixture, peas, curry powder and Fountain Mustard Sauce. Stir to combine and leave to cool.
Pre heat oven to 200°C. Line 3 baking trays with baking paper. Using a 10cm cutter, cut five rounds from each pastry sheet. Spoon 1 ½ tbsp of mixture over the center of one pastry round. Brush the edge with egg and fold up sides to enclose filling. Press edges to seal, mark with a fork, and place on prepared tray. Repeat with remaining mixture, pastry rounds and egg. Brush tops of pasties with egg.
Bake, rotating trays half way through cooking, for 20 minutes or until golden. Serve warm with extra Fountain Mustard Sauce or Fountain Tomato Sauce.