1. In a deep, heavy skillet over medium-high heat, melt butter in the vegetable oil, and sear the ribs on all sides. A couple of minutes per side will allow them to become nicely browned. Remove from pan and set aside.
2. Reduce the heat to medium. Add the onions, carrots, mushrooms and celery to the pan and cook for several minutes, scraping up any browned bits from the bottom of the pan.
3. Add garlic, bay leaves and thyme, and continue to cook until the garlic is fragrant.
4. Add wine to de-glaze pan, again, scraping the bottom of pan to get up any of the crisp tidbits left behind.
5. Add stock, stir well and bring to boil.
6. Place seared short ribs in a crock pot or slow-cooker and carefully pour liquid and vegetables from pan over short ribs.
7. Set slow-cooker to "high", cover and allow to cook for four hours.
8. After four hours, remove short ribs from slow-cooker and set aside.
9. Using an immersion blender, blend remaining liquid and vegetables into a thickened sauce. Taste for seasoning and adjust accordingly.
10. Pour sauce over short ribs and serve with garlic smashed potatoes.
These are some of the most moist and tender slow-cooked short ribs you will ever try. Served best with Garlic Smashed Potatoes!