In large saute pan heat olive oil over medium heat add onions and saute until translucent. Remove onions and set aside.
Divide chicken breasts in half.
On a hard surface such as a cutting board, place a layer of wax paper or plastic wrap to cover surface. Place separated breasts on covered board and place another layer of wax paper or wrap on top of breasts. Using meat cleaver or rolling pin, pound/roll out meat to ¼ inch thickness.
In medium size shallow bowl, place flour and mix in ground peppercorn. Dredge each breast in flour.
Saute breasts for three minutes on each side, be sure to add more olive to pan if necessary. Remove breast from saute pan and cover with foil.
To the saute pan add chicken stock, butter, wine, lemon juice, capers and onions. Stir well and bring to boil.
Reduce to simmer, add breasts and continue to simmer for 3 to five minutes. Remove breasts to serving platter(s), pour sauce over chicken.
If necessary, add a pinch of flour or thickening agent to sauce if it appears to thin after removing chicken.
Serve immediately and most importantly, savor the flavor!