Roberto Santibañez's "Truly Mexican" cookbook has a recipe for authentic Mexican pork carnitas that can be made either in a slow cooker or on the stove top. It uses 4 pounds of fatty pork shoulder cut into 2-inch pieces and should serve eight people.
First, combine the pork in a slow cooker or a large, heavy pot with 3 cups of cold water, 1 medium white onion cut into thin slices, 1/2 of an orange cut into two wedges and 1/4 cup of lard or vegetable oil. To this, add 8 cloves of garlic, 3 bay leaves, 1 tablespoon sweetened condensed milk, 2 teaspoons of dried Mexican oregano and 1 1/2 to 2 teaspoons of fine salt or 3 to 4 teaspoons of kosher salt.
If making the carnitas on the stove top, bring all of the ingredients to a boil, and skim any scum off the surface. Bring it down to medium-low heat, and let it simmer rapidly until the liquid evaporates and the pork becomes tender, which should take approximately one and a half to two hours. Throw away the orange pieces and bay leaves, and preheat the oven to 450 degrees Fahrenheit. Place the pork in an oven-proof container, put it into the oven uncovered for twenty to thirty minutes until nicely browned, and then serve.