Add the milk, garlic, shallot, lemon zest, thyme, bay leaf, and red pepper flakes to the pot. Bring the milk to a simmer, then cover the pot and transfer to the oven. Braise the pork, turning it over every 30 minutes or so, until very tender when pierced with a knife, 3 to 3½ hours. Uncover the pot and place on top of the stove.