2 TBSP olive oil
1 3 to 4 lb pot roast (chuck, bottom round, or rump roast will work)
2 large onions, quartered
2 celery stalks, thinly sliced (2 cups)
2 large carrots, thinly sliced (2 cups)
3 garlic cloves, minced
1 6 oz can tomato paste
1 ½ oz pkg dried mushrooms (such as Portobello or shitake)
1 TBSP salt
1 tsp dried oregano
1 28 oz can whole plum tomatoes, chopped, liquid reserved
Heat the oil in a large skillet over medium-high heat and brown the roast on all sides. Transfer the roast to a 4- to 6-quart slow cooker. To the fat remaining in the skillet, add the onions, celery, carrots, and garlic. Cook, stirring frequently, until tender, about 10 minutes. Add the tomato paste and stir to coat the vegetables; transfer to the cooker. Add mushrooms, salt, oregano, and tomatoes (plus 1 cup of their liquid). Cook 8 hours on low heat, or 4 hours on high heat.
Serve with mashed potatoes or pasta.