Sprinkle roast with 1 tablespoon kosher or sea salt and rub it in on all sides and ends. Wrap tightly in plastic wrap and remove from fridge and bring to room temperature about 60 minutes when ready to cook. Refrigerate for at least 18 hours or up to 24 hours.
Rinse roast thoroughly under cool running water to remove as much of the salt brine as possible.
Pat roast dry with paper towel.
Turn crock pot on high. Prepare slow cooker with light coating of cooking spray. Add broth and tomato paste. Stir until blended. Add sliced onions to middle of crockpot.
In a large bowl add 2 tablespoon oil, 1 ½ tblsp yellow or dijon mustard, ½ tblsp garlic powder, ½ tblsp plus ½ teaspoon paprika, ½ teaspoon thyme, 1 tblsp onion powder, ½ tblsp Montreal Steak Spice, ½ tblsp Italian Seasoning, ½ tblsp curry powder, ½ tblsp pepper. Stir until blended.
Really rub and flip roast in large bowl until evenly coated with seasoning. Put excess seasoning on top of roast (fat side up) and place roast on top of onions and broth mixture. Reduce heat to low.
Cover and continue to cook on low heat until meat registers 125 degrees (for medium-rare), maybe check at 1 ½ hours. Usually between 2 and 2 ½ hours.
Transfer roast to carving board, tent with foil, and let rest for 15 to 20 minutes. Turn crock pot on “high” Remove ¼ cup spoonful of broth to measuring cup, add flour and stir until lump free.
Return to slow cooker gradually and Whisk. Cook for several minutes until thickens. Add butter and parsley into gravy and season with salt and pepper to taste. Slice roast thin against grain and serve with gravy.
Add butter and parsley into gravy and season with salt and pepper to taste. Slice roast thin against grain and serve with gravy.