Melt the butter in a saucepan, remove from the heat, and stir in the flour. Add the milk and cream and bring to a boil over high heat, beating constantly with a whisk until the sauce is smooth and thick.
Let it simmer for a minute then set aside to cool. Cut the liver into chunks. Roughly chop the pork fat and mix both with the chopped onion and anchovies. Divide the mixture into thirds. Pure each batch in an electric blender set at high speed, adding enough sauce to keep the mixture from clogging the blender.
Transfer each completed batch to a large bowl and beat in any remaining cream sauce. (To make by hand, first have the butcher grind the liver and pork fat together, 3 times, very fine, then combine with the cream sauce, beating them together thoroughly.)
Beat the eggs well with the salt, pepper, allspice and cloves and mix thoroughly into the liver mixture. The blender mixture will be considerably more fluid that the one made by hand.
Preheat the oven to 350F. Line a 1-quart loaf pan or mold with the strips of pork fat. Arrange the strips lengthwise or crosswise, making sure they overlap slightly and cover the bottom and sides of the pan.
If long enough, let them hang over the sides; otherwise, save enough strips to cover the top. Spoon the liver mixture into the loaf pan and fold the overhanging strips (or extra strips) of pork fat over the top. Cover with a double thickness of aluminum foil, sealing the edges tightly, and place in a large baking pan.
Pour into the baking pan enough boiling water to reach at least halfway up the side of the load pan and bake the liver paste in the center of the oven for 1 1/2 hours.
Remove from the oven and lift off the foil. When it cools to room temperature, re-cover with foil and chill thoroughly. Liver paste may be served in 1/2" thick slices as a first course, luncheon dish, or on bread as smorrebrod.