Slice chicken breasts in half or thirds. If sliced in half, use a mallet to pound the chicken breasts into ½ inch thickness. Sprinkle salt and pepper on both sides of the chicken.
In a small bowl, combine the chicken broth, lemon juice, garlic, and red pepper flakes.
Heat the olive oil in a large skillet over medium high heat. Add the chicken and allow to brown on both sides for 4-5 minutes per side.
Remove the chicken to a plate.
Reduce the heat to medium, add the shallots or red onions to the skillet along with the lemon and chicken broth mixture. Using a whisk, scrape the bottom of the pan so all the brown bits are loosened. Increase heat back up to medium high and let sauce come to a simmer. Continue to cook the sauce for 10-12 minutes or until the sauce is reduced by 1/2.
When the sauce has thickened, remove from heat, add the butter and whisk until it melts completely. With the skillet off the heat, add the heavy cream, whisk to combine.
Add the chicken back into the pan and drizzle the sauce over the chicken. Cover the skillet and simmer on medium heat 5-8 minutes or until the chicken is completely cooked through, but do not bring to a boil otherwise you risk curdling the cream. Top with chopped parsley and grated parmesan (optional). Serve over pasta or with a side of steamed vegetables.