One pan is all you need for this savory, and super easy, chicken with mushroom sauce that's on the table in 30 minutes or less.
Heat a large skillet to medium high heat. Add 1/2 tablespoon of butter and 1/2 tablespoon of the olive oil until the butter is melted then add 3 of the chicken breasts to the pan. Cook undisturbed until you can see that the chicken is cooking through on the one side, about 3-4 minutes. Use tongs to flip the chicken over once it is nicely browned and cook for an additional 3-4 minutes or until the thickest part of the chicken reaches 160 degrees F. Transfer to a plate and tent with aluminum foil to keep warm and rest.
Wipe out the pan with paper towels and add 1/2 tablespoon of butter and the remaining olive oil. Repeat with the remaining three chicken breasts. Transfer to the plate with the other cooked chicken.
Wipe out the pan again and over medium heat, and melt 1 tablespoon of the butter. Add the mushrooms and leeks to the pan with a pinch of kosher salt. Cook while stirring occasionally for about 5 minutes or until the mushrooms are softened and the leeks are becoming limp.
Add the wine and continue to cook for 2 minutes. Add the cream or half and half, raise the heat to medium high and cook for 5 minutes or until the cream coats the back of a spoon and has slightly reduced. Stir in the last tablespoon of butter to add a bit of gloss and adjust the seasoning to taste.