Preheat your oven to 350 degrees. Combine ketchup, onion, molasses, maple syrup, vinegar, Worcestershire, mustard, and pepper in small to medium sized bowl. Set aside.
Season chicken with salt and pepper. Heat oil in an ovenproof or regular skillet until it shimmers or a drop of water flicked in it dances. Brown each chicken breast until golden brown, about 4 minutes per side. Transfer chicken to plate and set aside. Wipe oil out of the skillet with paper towel.
Add sauce to skillet with garlic and scrape up browned bits on bottom of skillet with a wooden spoon. Simmer sauce over medium heat, stirring frequently until sauce has thickened, about 8-10 minutes.
Return chicken to your oven-proof skillet or use another pan for the oven and adjust chicken to totally coat with the sauce. Spoon extra sauce over each piece to create a thick coating of sauce. The thicker the better.
Place skillet in oven and bake for 12-15 minutes, or thickest part of chicken breast is about 135-140 degrees.
Set oven to broil and remove chicken from oven.
Baste or spoon more sauce over chicken breasts if desired. Throw the skillet back in the oven for another 5-10 minutes, or chicken is 165 degrees at its thickest point. It doesn't matter if your oven hasn't reached broil yet, still throw it back in the oven. Chicken will bubble on top. Wait until it is bubbling everywhere before you take it out of the oven.
Transfer chicken on to a plate and let rest 5 minutes. Meanwhile, scrape all of the sauce out of the skillet and into a bowl to serve separately with the chicken.