Start with the filling: Place the chicken in a saucepan. Add water to cover. Add the garlic, carrot, bay leaf, parsley and half the onion. Bring to a boil. Reduce heat. Cover. Simmer until the chicken is tender (about 30 minutes). Let cool in the broth.

Remove the meat from the skin and bones. Shred the chicken meat. Cover to prevent it from drying out. Set aside. Strain the broth. Set aside. Combine the sour cream with the heavy cream. Let stand at room temperature for 30 minutes to thicken. Shred the cheese. Set aside.

Slice the remaining onion. Rinse with cold water. Set aside 2 slices of onion per serving. Add the left over onion to the broth. Combine the shredded chicken with half of the shredded cheese. Set the remaining cheese aside. Add 1/4 of the sour cream to the chicken and cheese mixture.

Blend carefully. Heat about 1" of oil in a large skillet (one big enough to hold an unrolled tortilla flat) to 300 degrees. Pass the tortillas, one at a time, through the oil (to soften and seal them). Press between paper towels to remove excess oil. Divide the filling equally between the tortillas. Roll each up and place, seam side down, in a buttered casserole dish. Keep covered while preparing the sauce. Preheat the oven to 400 degrees.

Remove the husks from the tomatillos. Wash off any sticky residue. Combine the tomatillos, chiles and minced garlic. Puree (a food processor will do this best). Place the mixture in a saucepan. Bring to a boil. Stir in the sugar, salt, pepper and the measured amount of the chicken broth. Keep hot. Cover the tortillas in the baking dish. Bake until heated through (about 10 minutes). Cover with the sauce. Top with the reserved shredded cheese. Bake, uncovered, until the cheese melts (5-8 minutes). Garnish with the reserved onion slices and the crumbled cheese. Serve at once with the remaining (room temperature) sour cream mixture.