Mashed Potatoes with Ham - With meat

2 whole garlic heads 1/4 cup butter , softened 1 tablespoon shallot , finely chopped 2 teaspoons rosemary , finely chopped 2 1/2 lbs red potatoes or 2 1/2 lbs[...]

1/2 lb celery root , peeled and cut into 1-inch chunks 1 large baking potato , peeled and cut in half 1 garlic clove , peeled 2 tablespoons milk 1 tablespoon[...]