Preheat your oven to 400°F and line a baking sheet with parchment paper.
Peel the Yukon Gold potato and dice into 1-inch chunks.
Place the potato chunks in a pot of cold salted water, bring to a boil, and cook for 12-15 minutes until fork-tender.
While potatoes cook, rub the chicken breast with olive oil, dried rosemary, sea salt, and black pepper.
Place the chicken and broccoli florets on the prepared baking sheet and roast for 18-20 minutes until the chicken reaches an internal temperature of 165°F.
Mince the garlic cloves and sauté them in a small pan with the ghee over low heat for 1-2 minutes until fragrant but not browned.
Drain the cooked potatoes thoroughly and return them to the warm pot.
Add the sautéed garlic ghee and the Greek yogurt to the potatoes.
Mash the mixture using a potato masher or fork until the texture is smooth and creamy.
Plate the velvety mashed potatoes and top with the sliced roasted chicken and broccoli.