1Preheat oven to 200 C. Line oven tray with baking paper.
2In a food processor, pulse mushrooms until finely chopped. In a frying pan, melt butter on medium. Saute mushrooms and eschalots 4 to 5 mins. Stir Dijon through. Cool.
3In a large bowl, combine sausage mince, pork and veal mince, breadcrumbs, egg and rosemary.
4Place 1 pastry sheet on a clean work surface. Brush one edge with egg. Place remaining ½ sheet pastry alongside, slightly overlapping edges. Press edges together to seal.
5Arrange prosciutto slices along centre of pastry on a slight angle. Spread with mushroom mixture. Press sausage mixture on top, forming into a log. Place on tray.
6Fold pastry over mixture to enclose, pressing to seal and trimming any excess. Roll so Wellington is seam-side down.
7Brush pastry with remaining egg and make 3 cuts in top to allow steam to escape. Bake 40 to 45 mins until puffed and golden. Serve with steamed veggies and barbecue sauce.
Defrost frozen Wellington in fridge overnight and bake as directed.
Photos: Rob Shaw/bauersyndication.com.au