Preparation

Make the filling:

• In a small bowl, combine the sugar, cornstarch, nutmeg, and cloves. Melt the butter in a heavy 4-quart saucepan over medium heat. Stir in the molasses, vanilla, and sugar mixture. Cook, stirring with a wooden spoon, until the sugar is dissolved, about 2 minutes. Add the plums and stir to combine well. Raise the heat to high and bring the mixture to a boil. Cover the pan, reduce the heat to medium, and cook for 3 minutes, stirring occasionally, just to partially cook the plums. Remove the pan from the heat and set aside, uncovered, until needed.
• Position rack in the lower third and bottom of the oven; heat the oven to 425°F.

Make the biscuits:

• In a large bowl, whisk the flour, cornmeal, sugar, baking powder, baking soda, and salt to blend. Add the butter pieces and cut them in with a pastry blender or two table knives until the butter pieces resemble small peas. Add the sour cream and work it into the flour mixture with a rubber spatula until you have several large lumps of dough that appear quite dry. Turn the shaggy-looking mixture out onto an unfloured work surface and use both hands to quickly knead the clumps of dough just until they gather into one mass. The dough will be stiff and only slightly sticky. Shape the dough into a 4×6-inch rectangle. Lightly flour your work surface. With a long side of the dough nearest you, roll the dough into an 8×12-inch rectangle. Turn the dough over from time to time during the rolling and dust it lightly with flour if it’s sticky. Square the edges of the dough with your fingertips to keep it in a neat rectangle.
  Starting with a long end, use both hands to gently roll the dough up like a jelly roll.

• 刷与融化的黄油面团。搅拌的sugar and cinnamon in a small bowl to combine and sprinkle it evenly over the dough, leaving a 1-inch margin at the dough’s farthest edge uncovered. Roll up the dough like a jelly roll, starting with the long edge nearest you. Pinch the seam’s edges to seal. With the seam side facing down, cut the roll with a sharp knife into twelve 1-inch slices.

Assemble and bake:

• Pour the plum mixture (which may be warm or hot) into a wide baking dish (about 8×12 inches, or 2-1/2 quarts, so the biscuits will fit in a single layer). Arrange the bizcuits, cut side up, over the fruit mixture, leaving an inch or so of space betwen the bixcuits. Put the pan in the lower third of the oven and set a baking sheet lined with aluminum foil on the rack below to catch any juices which might bubble over. Bake until the biscuits are well browned and the juices are very bubbly, 25 to 30 minutes. Put the pan on a rack to let cool. Serve warm or at room temperature.