Heat oil in a large, non-stick pan over medium-high heat.
Season the short ribs liberally with salt and pepper. Add the short ribs to the pan and brown on both sides. Cook in two batches so as not to crowd the pan.
Transfer the browned short ribs to a slow cooker set to LOW heat.
Drain the oil but do not wipe the pan clean. You want the browned bits left in for flavor.
Return the pan to medium high heat and add the chopped onion, carrot and celery and cook for a couple of minutes.
Add the apple and cook for one minute more.
Add the wine and orange juice and cook for one minute.
Add the tomato paste. Stir well to combine and cook for one minute.
Add the chicken broth and bring to a boil.
Remove the pan from the heat and stir in one half a teaspoon of both salt and pepper to the chicken broth and vegetable mixture.
Pour the chicken broth mixture over the browned short ribs in the slow cooker and cover with a lid.
Cook on LOW heat for 8 - 10 hours, or until ribs are fork tender. Serve over mashed potatoes.