Season short ribs with salt and pepper on all sides.
Heat skillet over high heat and add butter and oil. Once the skillet is very hot, carefully add short ribs. Sear ribs on all sides for about 30 seconds until you have a nice crust. Transfer seared ribs to your slow cooker.
In the same skillet you cooked the short ribs, add remaining ingredients and bring to a simmer. Simmer for about 10-15 minutes.
Carefully pour red wine sauce over the short ribs.
Cook in your slow cooker on the low setting for 8 hours or on high setting for 4 hours.
When done, transfer short ribs to a plate. To thicken the sauce, pour 1 cup of the sauce into a bowl and whisk in a tablespoon of cornstarch. Pour sauce back into the slow cooker and stir to combine.
Pour sauce over short ribs and serve.