Mix flour, salt, sugar, yeast, milk, and eggs in a mixer for two minutes on slow speed.
Increase speed and mix for 8 minutes until the dough is elastic.
Incorporate softened butter into the dough for five minutes while scraping the bowl.
Chill the covered dough in a bowl overnight.
Preheat your oven to 200°C.
Knock air out of the dough and roll into a 5mm thick circle.
Layer half the prosciutto, then cranberry sauce, brie slices, and the remaining prosciutto on the dough.
Seal the dough over the filling to encase it completely.
Place the parcel seam-side down on a tray, glaze with egg, and score a pattern.
Bake for 25 minutes until golden-brown.