Brown hock in bacon fat in a large pot, then add onion and sauté until golden brown. Add garlic and reduce heat. Fold in mustard greens gradually. Water from washing will wilt greens slowly. When almost wilted, just cover with chicken stock and add red pepper flakes. Bring to a simmer and cook for an hour or more. Add cream and continue cooking until greens are very soft. Season with salt and pepper.
