As like many fruit butters, the fruit is simmered with sugar and spices until it forms a gooey, sweet spread. Although no exact measurements were given to me, and you'll find as well you won't need them, I've included my measurements below.
There are English/American versions of plum butter. The American or English recipes I've come across include nutmeg, cloves, hints of orange, and cinnamon. The two German varieties I've tasted, including Thekla's, are made only with cinnamon and sugar.
Stainless steel or cast iron oven safe pot
11 large plums, about 2.5 pounds
1 cup granulated sugar (less or more to taste)
1 tsp cinnamon (or more to taste)
1 cup of water (enough water to cover the surface of the plums by 1")
Yield: 1 1/4 pints
Stone the fruit, and chop the fruit into 1" or small pieces. Leave the skin on. Place plums in an oven safe baking dish, and add the cinnamon and sugar. Stir to combine. Pour water on top to cover plums by about 1". Cover and bake, 325 degrees for 4-5 hours. Stir occasionally, and vent the lid during the last hour of cooking. The plums will break down and form a gooey, thick spread. More baking time might be needed. When the color turns a dark brown and the texture is thick, it is ready to remove from the oven and cool. If you use red plums the change in color will be easier to notice. Upon removal from the oven I spooned the Pflaumenmus into sterilized canning jars and placed them inside the refrigerator.
Spread on bread and toast. I would imagine it also would work well used as a chutney for meat.