Years ago I went to the farm of an elderly fruit farmer. I said I wanted Italian plums with which to make my grandmother's recipe for plum tart (Zwetschgenkuchen). She gave me a funny look and said "You mean fresh prunes, and you don't want Italian because they are not sweet enough to make dried prunes that can be sold. You want a sweeter variety like French prunes or Sugar Prunes." She handed me a paper bag and directed me to an orchard.
Silly me. A plum is not necessarily a plum. It wasn't that day that I learned the difference between a plum and a fresh prune. Plums originally come from Asia and prunes come from Europe. A plum is usually rounder and redder, inside and out, than a fresh prune which is blue or purple on the outside and yellow on the inside. For Asian plums, many of the newer varieties were bred by Luther Burbank, think Santa Rosa, Satsuma,Mariposa, Kelsey, Red Beauty. For European plums or prunes or whatever you want to call them, think Damson, Italian, French, Sugar, Stanley, and Imperial. With the European varieties no matter what you call then someone could argue that you are using the wrong term, so I vote for telling them to shut up and eat.
You might have already guessed from my mention of a paper bag into which I was supposed to put the fruit: that old lady is dead and her farm is a housing development. And that is progress. I can still get fresh prunes, but no variety is indicated, and I now sprinkle a little sugar on the cut fresh prunes before I put it into the oven.
2 cups flour
2/3 cup sugar
8 tablespoons (1 stick) sweet butter, cut in chunks
1 teaspoon grated fresh lemon peel
1/8 teaspoon cinnamon
1 whole egg
1 egg yolk
2 pounds Damson (prune) plums
1. Place flour, sugar, butter, lemon peel and cinnamon in food processor and mix until grainy.
2. Add the egg and the yolk and process until the dough forms one large ball. If it doesn't, press it into a ball by hand.
3. Allow the lump of dough to sit uncovered for an hour. Then roll out on a floured board and transfer to a torte base form.
4. Cut the plums into quarters. Remove and discard the pits. Cover the tart base with plum quarters, overlapping slightly, starting with a ring of plums at the outer edge and filling in toward the center. Sprinkle on a little sugar.
5. Bake at 350 degrees until crust starts to brown and the plums start to bubble, about 50 minutes.