Make "stale" breadcrumbs by processing one- or two-day-old bread.
Preheat the oven to moderately hot 200°C Line 2 oven trays with baking paper.
Heat butter in a large frying pan and add the onion and carrot. Stir for about 5 minutes, until the onion has softened. Combine the onion mixture, tomato sauce, parsley, sausage mince, beef mince, breadcrumbs, salt and pepper in a large bowl. Mix thoroughly.
Place a sheet of thawed pastry on a board and cut in half.
Place one sixth of the mince mixture along the centre of the pastry.
Roll the pastry over to enclose the mince mixture. Cut this into 3 pieces.
Repeat with remaining pastry and mince mixture.
Place sausage rolls on prepared trays. Brush with milk.
Bake for about 15 minutes or until browned lightly.