Heat the oven to 350°F. Put the sliced sweet potatoes in a medium saucepan with the water, sugar, cinnamon and ginger. Bring to a boil, reduce the heat to a simmer and cook uncovered for 10 to 12 minutes, until the potatoes are still firm but tender. Do not drain.

In a bowl, mix the self-rising flour, cinnamon and 1/2 cup brown sugar. Cut in the cold butter with a pastry blender or two large dinner forks. Slowly pour in the milk while stirring, until the mixture is combined. The dough will be crumbly and slightly sticky; use only as much milk as you need.

Spray a 9x13-inch baking dish with nonstick cooking spray. Crumble about a third of the dough into the bottom of the dish. Lift the potatoes out of the pan with a slotted spoon and spread them evenly in the dish. Measure 1 cup of the cooking liquid and pour it over the potatoes. Crumble the remaining dough over the top and sprinkle with the 2 tablespoons of brown sugar.

Bake for about 40 minutes, until the top is golden brown and the dough is cooked through.

Let the cobbler rest for about 10 minutes so the sauce can thicken, then serve warm.