Place the potatoes in a large saucepan. Add enough cold water to cover by 1 inch; bring to a boil over high. Season with salt, reduce the heat to medium and simmer until tender, about 20 minutes.
Meanwhile, in a small saucepan, toast the spices over medium, stirring often, until fragrant, 1 to 2 minutes. Add the half-and-half and butter; bring to a simmer, stirring until the butter melts. Season with salt and pepper. Remove from the heat; cover and let steep until flavors infuse, about 10 minutes. Strain through a fine-mesh sieve; discard solids.
Reserve 1 cup of the potato cooking water; drain. Press the potatoes through a potato ricer into a large bowl or transfer to a bowl and mash with a potato masher or electric mixer. Mix in the hot half-and-half just to blend. Fold in the yogurt. Add reserved cooking water by the tablespoon if too stiff; season. Sprinkle with the cilantro.
