Any version of a drop dumpling or biscuit makes a lovely slump.
Make the filling: In a 12-inch cast-iron dutch oven over medium-high heat, combine sugar and salt with ⅓ cup water. Bring to a boil, stirring until sugar and salt dissolve. Add boysenberries and ginger; cover dutch oven and bring mixture to a boil. Reduce heat to medium-low and simmer until slightly thickened, about 10 minutes.
Make the dumplings: In a medium bowl, whisk together flour, sugar, baking powder, salt, and black pepper. Add buttermilk and butter, stirring until batter is combined and smooth. Remove lid on dutch oven and gently drop rounded spoonfuls of batter evenly over fruit mixture. Reduce heat to low and cover. Simmer until a toothpick or cake tester inserted in center of dumplings comes out clean, about 20 minutes. Dumplings should be fluffy and slightly golden brown. Remove from heat and let cool slightly. Serve with sweetened whipped cream.