Slowly whisk the milk into the mixture in the saucepan until well combined. Continue to saute until it thickens.
Remove from the heat and stir in the ranch dressing as well as salt and pepper to taste.
Pour the sauce mixture over the chicken in the baking dish.
Sprinkle 1 cup of the cheese over the sauce.
Layer the tater tots on top of the chicken mixture.
Bake for 20 minutes.
Remove and layer with the bacon crumbles and remaining cheddar cheese. Bake for another 15-20 minutes until the tater tots are cooked completely and crispy.
