In a large pot of lightly salted boiling water, cook the potatoes, garlic, and bouillon until potatoes are tender but firm, about 15 minutes. Drain. In a bowl, mash potatoes with sour cream and cream cheese, adding milk as needed to attain desired consistency.
Prior to serving, mix in butter and season with salt and pepper to taste; serve hot.
Can be put in a slow cooker for 2-3 hours.