In a large saucepan, bring 500 ml (2 cups) of water to a boil with the salt, brown sugar, and molasses. Stir. Add the remaining water and the pepper. Add the guinea fowl in the brine and refrigerate for 6 hours in the refrigerator.
With the rack in the middle position, preheat the oven to 200 °C (400 °F).
Remove the guinea fowl from the brine and dry thoroughly with paper towels.
Place the guinea fowl, breast side up, side by side in a baking dish. Brush with the butter. Pour the broth in the baking dish. Bake for about 1 hour and 15 minutes or until a meat thermometer inserted into the thigh, without touching bone, reads 82 °C (180 °F). Add broth, as and if needed, so there’s always about 250 ml (1 cup) at the bottom of the baking dish.
Serve the guinea fowl with its cooking juices and Mashed Sweet Potatoes and Roasted Brussels Sprouts with Pancetta and Hazelnuts.
The brine makes the guinea fowl juicier. However, do not let them in the brine for more than 6 hours, it would become too salty.