Grill peanuts in a saucepan over medium heat without oil until golden brown. Chop finely in a food processor with sugars, approximately 20 seconds. Set aside.
Mix cream of rice, rice flour, 4 T sugar, water (1 C if using banana leaves, 1 1/4 C if using foil) and oil (3 T oil or less if peanuts are green, 5 T if they are not green).
Spread 3/4 of the rice batter on your wrapping material (foil or banana leaves. Heap peanut mixture in a line down the middle, leaving rice batter exposed in equal amounts on both sides. Lift sides of wrapping almost fully up and pour remaining batter on top, then complete wrapping to seal entirely so liquid will not penetrate.
Allow to boil gently over medium-low heat in a large pot of water, partly covered, for 24 hours. Remove from water. Koba is served in thin round slices while still warm.
REMARKS: This recipe is tricky because so much depends on the freshness of the peanuts and how you wrap the koba.
Most “raw” peanuts sold in stores are already rather old, while green peanuts are pulled from the ground within a week. If your koba falls apart or the peanuts remain tough, they were probably on the old side. The addition of peanut oil to the batter is not traditional but helps compensate for old peanuts.
Banana leaves are preferable because they allow steam to pass into the koba, which helps keep it properly moist, creating a dense, smooth, pâté-like texture. Tin foil blocks this moisture but requires less practice to wrap tightly.