Preheat the oven to 350°F. Lightly butter an 8-x-11-inch casserole dish or 10-inch Dutch oven for a thicker casserole - or a 12-inch Dutch oven or 9x13-inch casserole dish.
Place the potatoes in a large saucepan or pot and cover with water. Bring the water to a boil over high heat. Boil the potatoes about 25 minutes, or until they are fork-tender.
Remove the potatoes from the heat and drain. Mash until smooth.
Beat in 1 cup of the brown sugar, 1 stick of the butter, the half-and-half, and the eggs. Mix well.
Scrape the potato mixture into the casserole dish and spread evenly.
In a medium bowl, stir together the remaining 1 cup brown sugar, the flour, cornbread mix, and pecans. Stir in the remaining 1 stick butter and the warm water. Mix well.
Spoon the pecan mixture evenly over the potatoes and spread out evenly.
Bake for 30 to 35 minutes, or until the top is golden brown and a light crust forms. Serve warm.