Whip the mince together in the kitchen aid to emulsify the fat and the protein.
Sweat the onions in the butter with the salt for 15 mins until softened, then remove from the heat and add the herbs.
Mix the pork with the onions and remaining ingredients. Fry a little mix to cook through and check for seasoning.
Place in a piping bag and pipe into puff pastry, roll over and seal.
Cut into 15cm (~6 inches) lengths and place on a baking tray lined with parchment.
Mix the egg yolks and milk together, and brush the sausage rolls all over.
Leave for 30 mins then repeat to guarantee an attractive glaze.
Bake for 20 mins at 200° C/ 390° F in a preheated oven, then turn the trays and bake for another 15mins at 180° C/ 356° F.
Leave to cool for 15 mins, then trim the edges and serve with a generous helping of homemade piccalilli.