Season trimmed center-cut chops well with salt, pepper, garlic salt, onion powder, and Lawry's Seasoning salt. Heat 2 TBSP of vegetable oil in a pan over medium-high heat. Brown chops well on both sides and remove to slow cooker.
Thinly slice 2 large onions and place into pan with an additional 1 TBSP of oil. Add in 1.5 tsp of dry mustard, 1/2 tsp salt, 1/4 tsp ground black pepper, and 1/4 tsp cayenne pepper. Stir well and cook over medium-low heat until onions are cooked, caramelized, and developed in color.
Add to skillet 1.5 TBSP of minced garlic. Cook 1 minute, stirring frequently. Add 3 TBSP of flour. Stir until well combined and cook 2 minutes. Add 3/4 cup of white wine and 2 TBSP apple cider vinegar. Cook until thickened and pour over chops in slow cooker.
Cook 6-7 hours on medium, or 4-5 hours on high. Check approximately 1 hour before end of cook time as total cooking time will depend on your particular model of slow cooker.
When chops are fork tender remove from cooker. Add in 2 TBSP Dijon mustard and 1/2 cup heavy cream. Stir well and pour over chops on serving plate.