Peel the potatoes and cut them in half crosswise (quarter them if large). Cover them with cold water by 2 inches in a 3-quart saucepan and simmer until just tender, 15 to 20 minutes, depending on the size of the potatoes. Drain in a colander and return to the pan to let them dry slightly, about 2 minutes. While they are still warm, mash the potatoes using a potato masher or a ricer and keep them warm, covered.
Heat the oil in a 10-inch skillet over moderate heat until it shimmers. Add the chana dal and saute until light golden, about 1 minute. Add the onion, butter and turmeric and cook the mixture, stirring, until the onion is translucent, about 3 minutes. Add the cream and milk and cook until the mixture is reduced by half, about 7 minutes.
Meanwhile, whisk together the dry mustard and honey in a small bowl. Whisk in about 1/4 cup of the cream mixture, then whisk the honey mixture, salt, and pepper into the reduced cream mixture. Heat the mashed potatoes over low heat until warmed through and add the cream mixture, stirring until well combined. Season with salt and pepper.
Chef Floyd Cardoz, Tabla, Adapted from One Spice, Two Spice