Preheat your oven to 450°F.
Place potatoes in a medium saucepan and cover with water. Salt the water. Bring to a simmer over medium heat and cook, uncovered, till tender (about 20-25 minutes). Drain and cool. Cut into ½-inch pieces and set aside.
In a large pot, melt ¼ cup butter over medium heat. Add yellow onions and garlic and cook until tender, about 5 minutes.
Add chicken stock, carrots, celery, 2 teaspoons salt, and pepper. Bring to a simmer, lower heat and cook, partially covered, about 15 minutes. Stir in the heavy cream, raise the heat slightly, and cook for about 10 more minutes or until vegetables are tender.
Meanwhile, in a small bowl, mash together the remaining soft butter (½ cup) and flour until you have a smooth paste.
Lower the heat slightly and whisk in the floury paste with the vegetable mixture a little at a time. Stir in chicken, potatoes, pearl onions, peas, corn, hot sauce, and nutmeg. Simmer until thickened, about 10 minutes.
(You can prepare this filling a day ahead, remove from heat, cool, cover and refrigerate. Re-warm before using.)
Place the chicken filling into a buttered rectangular 9"x13" glass baking dish (3 quarts capacity). Or you can put the filling in ramekins if you wish. Make biscuits (directions below).
Place biscuits atop the filling, spacing them evenly apart. Brush top of biscuits with buttermilk. Place baking dish on top of a half-sheet pan and bake until the biscuits are golden brown and the filling is bubbly (about 15 minutes). Serve warm.