Peel and cube the russet potato, then place in a pot of water and boil until tender, approximately 15 minutes.
While potatoes boil, season the chicken breast with sea salt, black pepper, dried rosemary, and dried thyme.
Heat ghee in a skillet over medium heat and sear the chicken until golden and cooked through, about 6-7 minutes per side.
Mince the garlic cloves and add them to the skillet with the chicken during the final 2 minutes of cooking to soften.
Drain the cooked potatoes and return them to the pot.
Add the Greek yogurt, skim milk, and the sautéed garlic from the skillet to the potatoes.
Mash the mixture until smooth and velvety, adjusting consistency with an extra splash of milk if needed.
Slice the chicken breast and serve it immediately over the warm garlic mashed potatoes.