1) Arrange a rack in the lower third of the oven. Preheat the oven to 350 degrees.2) Cream the 1 cup sugar and stick of butter, either by hand or with a mixer. Add the flour, baking powder, eggs and salt, and mix well. 3) Scoop into a 9- or 10-inch buttered springform pan. (A springform pan is a baking pan with a clamping side/rim that detaches from the pan’s bottom.) Smear the batter so it fills the pan evenly. Arrange the plum halves on top, skin side down. 4) Mix the cinnamon with the remaining 1 or 2 tablespoons of sugar and sprinkle over the top.5) Bake for 40 to 50 minutes, until a toothpick inserted into the center pulls out clean. Remove and cool. Use a butter knife to separate the torte edge from the springform, then unclamp and remove the side.