Pound chicken breasts to an even thickness; do not pound them too thin.
In a nonstick skillet heat olive oil over medium-high heat.
Add onions and cook for 3 to 4 minutes, or until translucent.
Stir in garlic and continue to cook for about 30 seconds, or until fragrant.
Transfer to serving plate and set aside.
Season chicken breasts with salt and pepper.
Place skillet over medium-high heat and add 2 tablespoons olive oil.
When oil is hot, add chicken breasts to the skillet and cook 7 minutes; flip and continue to cook for 5 to 6 minutes or until thoroughly cooked and browned on both sides.
Remove everything from skillet and transfer to a serving plate; set aside.
For the Sauce
Set up a double-boiler by adding an inch of water to a small saucepan.
Bring water to a rapid boil and lower to medium-heat.
Combine all the sauce ingredients in a heat-resistant mixing bowl that is a little larger than the saucepan.
Set the bowl over the saucepan, making certain that the bowl can't touch the water.
Whisk the sauce until the sauce is smooth and creamy, about 3 to 4 minutes.
If it's too thick (it should be slightly pourable) add a tablespoon of milk.
Taste and adjust accordingly.
Remove from heat and pour the sauce over the chicken breasts.
Serve.
Notes
Pound chicken pieces so that they are all about the same size. Do not pound them thin!Serve with pasta, rice, orzo, or a simple vegetable side dish.