Bring a large pot of water to boil. Add the potatoes and garlic cloves to the water, along with a large pinch of salt. Boil for 20 minutes.
While the potatoes boil, microwave the chicken stock for 2 minutes. Melt the butter separately. As the potatoes finish, reserve 1 cup of the boiling liquid and set aside.
Drain the potatoes and add them to a large mixing bowl with the butter. Use a hand mixer to beat the potatoes until they start to clump together. Add the mayo and continue to mix for a couple minutes.
Add the garlic powder, a couple pinches each of salt and pepper, and 1/4 cup of chicken stock and continue mixing. Add the stock every 30 seconds, 1/4 cup at a time, until you reach a consistency you like. If the potatoes are too dry, use some of the reserved boiling liquid. Season with salt and pepper to your preference. Use some of the ham jus in place of gravy (you can even thicken the jus if you want).