The 'Master' might be Thomas Rudstone, a popular astrologer, whose almanacks were published throughout the early 17th Century, containing prognostications and general information.
Original Receipt in 'The Compleat Cook' by 'WM', 1658 (WM 1658)Master Rudstones Posset.
Take a Pint of Sack, a quarter of a pint of Ale three quarters of a pound of Sugar, boyle all these well together, take two yolks of Eggs and sixteen whites very well beaten, put this to your boyling Sack & slice it very well together till it be thick on the coales; then take the three pints of Milk or Cream being boyled to a quart, it must stand and cool till the Eggs thicken, put it to your Sack and Eggs, and stir them well together, then cover it with a Plate and so serve it.