Preheat the oven to 375°F (190°C).
Preheat large stainless steel skillet over medium-high heat.
Add in olive oil and once oil is slightly smoking, gently place chicken breasts in skillet.
Sear for 4–5 minutes per side, or until browned.
Remove chicken and place on sheet pan or other oven-proof dish and place in oven.
Bake for 10–12 minutes or until chicken is cooked through.
Reduce skillet heat to medium.
Add butter to skillet, scraping up the browned bits from the chicken.
Stir in the garlic and sauté until fragrant (but not burned), then stir in mushrooms.
Sauté for 1–2 minutes, then add in sherry and chicken stock.
Let simmer until reduced slightly and mushrooms are cooked.
Add in chives just before serving.
Serve mushroom sauce over chicken.