Position a rack in the center of the oven and heat the oven to 400°F. Grease a 12-cup nonstick muffin tin with the butter.
In a 4-cup liquid measuring cup, thoroughly whisk the cream and eggs. Whisk in the horseradish, 1 tsp. salt, and a few grinds of pepper and set aside.
Portion half of the bread cubes evenly among the 12 muffin cups. Portion half of the parmigiano and half of the chives evenly among the cups. Repeat with the remaining bread, cheese, and chives.
Whisk the custard again and carefully pour it into the muffin cups, distributing it evenly. Refrigerate for at least 30 minutes.
Bake until the puddings are set and the tops are nicely browned and puffed, 18 to 22 minutes. Let cool in the pan for 20 minutes. Carefully remove the puddings from the pan, running a paring knife around the edge of the puddings if they stick.
Make Ahead Tips
The puddings can be assembled and refrigerated up to 6 hours before baking. They can also be baked a day ahead, refrigerated, and reheated, wrapped in foil, in a low oven.
nutrition information (per serving):
Photo: Scott Phillips