We recently made this for Easter and it has become a big hit!

3 T olive oil
2c white mushrooms
3 leeks, washed cut Julienne (white part only)
1 med onion
1/2 sour cream
1/2 half n half
1/2 shredded Cheddar cheese
( 1 oz) package of Dry Onion Soup mix
1/2 t paprika
1/4 t salt
1/4 t pepper
skinless, boneless chicken breasts ( 1 – 1 1/2 lbs)

Heat a large skillet over med heat, put oil, mushrooms, leeks and onion to pan. Cook 8 minutes stirring.. Remove from heat and add cool slightly. Stir in sour cream, half and half, cheese, soup mix, paprika, salt and pepper. Coat a 13 x 9 glass baking pan dish cooking spray. Arrange Chicken in pan. Pour cooled mushroom mix evenly over chicken. Cover with plastic wrap and refrigerate overnight. Preheat oven to 350. Remove plastic wrap and bake uncovered for 1 hour. variation on the recipe call for 3 bacon slices, cooked and crumbed over the top before refrigerating, with 2 T bacon fat replacing oil oil to cook mushroom/onions