Begin by patting the boneless, skinless chicken breasts dry using paper towels. Season both sides generously with salt and black pepper.

In a large skillet, heat 2 tablespoons of olive oil and 1 tablespoon of butter over medium-high heat. Add the seasoned chicken to the skillet. Sear for 4-6 minutes on each side until golden brown.

In the same skillet, reduce the heat to medium and add the remaining 1 tablespoon of butter. Allow it to melt and then add shallot and minced garlic. Sauté until translucent, about 2-3 minutes.

Carefully pour in ½ cup of Irish whiskey, scraping the bottom of the skillet to incorporate the brown bits. Allow the whiskey to simmer and reduce by half, about 3-5 minutes.

Add 1 cup of chicken stock and 1 tablespoon of Dijon mustard if using. Bring to a gentle simmer for 2-3 minutes. Stir in ¾ cup of heavy cream and allow to reduce until glossy, about 5 minutes.

Nestle the seared chicken back into the skillet and simmer on low for 3-6 minutes, until fully cooked through.

Whisk in 1 tablespoon of cold butter and add the juice of ½ lemon. Fold in parsley or chives and adjust seasoning with salt and pepper.

Plate each piece of chicken and spoon sauce over. Garnish with additional herbs and lemon zest.