Mix the chili powder, dry mustard, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a mixing bowl. Massage the dry rub into the pork. Cover and chill overnight, or place the pork into a large ziplock bag.
Drain and rinse the beans, add to a mixing bowl, and set aside; Preheat the oven to 450 degrees In a large cast iron saucepan, cook the bacon until crisp and drain the excess bacon grease. Add the garlic and cook for 1 minute, then add the beans and 1/2 teaspoon salt, and 3 cups of water. Heat for three minutes, and stir thyme into beans. If the beans get too dry, add a little water. Cover, set aside, and keep warm.
In the 10-inch cast iron skillet, heat the cooking oil over medium-high heat. Add the pork, and brown on all sides. Add beef stock to the skillet and place the skillet into the oven. Roast, uncovered, for 20 minutes or until a meat thermometer inserted into the thickest part of the pork registers 145 degrees. Remove from oven, put the pork on a cutting board, and tent with aluminum foil.
Add one tablespoon of butter to the pan juices in the skillet, and when melted transfer to a small bowl; set aside.
In the same skillet, heat the remaining one tablespoon of butter over medium heat, and add the spinach. Cook and stir until wilted, 1 to 2 minutes. Add salt and pepper to taste.
To serve, cut the pork into 1/2-inch pieces. Arrange beans in the center of the serving platter, and spoon the spinach on top of the beans. Spoon some pan juices around the beans on the platter, and arrange the pork slices on top of the spinach. Pass the remaining pan juices once the guests have plated their serving.A serving option is to plate individual servings following the sequence above Enjoy!
