Preheat the oven to 350 degrees F.
In a heavy saucepan, bring 4 cups of water to a boil. Add the tomatillos, chile and onion and boil them until the tomatillos' color changes to light olive.
Place the garlic cloves, chicken bouillon and cilantro in a blender. Add the boiled tomatillos, chile, onion and 1 cup of the boiling water. Process until smooth.
In a small bowl, add the whole milk to the sour cream and mix well, until smooth.
Heat olive oil in a large skillet. Make the tortillas pliable by frying them briefly in the oil, 5 - 10 seconds on each side, until you see air bubbling under the thin skin surface of the tortilla. They should not brown too much and they should still be pliable. Drain excess oil with paper kitchen towels.
Spread enough salsa verde, 1/4 to 1/3 cup, to cover the bottom of a large baking pan, big enough to accommodate all the stuffed, rolled-up enchiladas. Divide the chicken evenly between the tortillas, roll them up and place them at the bottom of the baking pan, seam side down and in just one layer.
Pour the rest of the sauce over the enchiladas. Drizzle with the sour cream mixture and evenly sprinkle the shredded cheese all over the enchiladas and the salsa.
Bake for 30- 35 minutes until bubbly and when cheese has started to brown. Serve immediately.