Preheat the oven to 375 degrees. In a medium bowl, whisk together 1 cup sugar, salt, and flour. Using a pastry blender, cut in the butter until the mixture resembles coarse meal. Set aside half the mixture. Add the cinnamon, baking powder, and 1 egg to the other half. Mix until well blended. Press into the bottom of a 9-inch shallow baking dish. Bake until firm and golden brown, about 15 minutes.
While the pastry is baking, whisk together 1/4 cup sugar, the remaining egg, the cream, and the almond and vanilla extracts in a small bowl; set aside.
Remove the pastry from the oven, and top with plum slices. Pour the cream mixture over the plums, and sprinkle with reserved butter-flour mixture. Sprinkle with the remaining 2 tablespoons sugar, and bake until topping is golden brown and the plums are tender, 20 to 30 minutes. Serve warm or at room temperature with whipped cream.