Spray a 6 quart crockpot with non-stick spray
Layer sliced onions on bottom of crockpot.
Season pork roast with salt and pepper and place roast on top of onions.
Place carrots and celery around roast.
Pour 1 cup white wine (or chicken broth) and 1 1/2 tablespoons white balsamic vinegar in crockpot.
Pour 1 cup chicken broth in crockpot. You want to add chicken broth till the liquid level is about halfway up the side of the roast. This means you may not use the whole 1 cup or you may need a bit more. I only needed the 1 cup.
Sprinkle the garlic, thyme, and rosemary over the roast.
Cook on low for about 7 - 8 hours or on high for 3 - 4 hours. Remove roast and vegetables from crockpot and cover with foil while you are making the gravy. Remove 2 cups of the liquid in crockpot to a medium saucepan. Discard whatever liquid is left in crockpot.
Gravy: With a fork, mix the flour and softened butter together to make a paste. Then whisk the mixture into the liquid over medium-high heat till the gravy is thickened the way you would like. Season with salt and pepper. Remove from heat.
Place roast and vegetables back into the crockpot and pour gravy over roast. Let heat for another 30 – 45 minutes and serve. The pork roast will be tender enough to shred, if desired or just slice.