Heat 1 Tbsp olive oil in a large heavy bottomed skillet over medium-high heat. Working with half of the beef at a time, dab both sides dry with paper towels and season with salt and pepper to taste.
Sear in skillet until browned, turning once halfway through, about 4 - 5 minutes total. Transfer beef to slow cooker. Add an additional 1 Tbsp oil to skillet, repeat with remaining beef. Leave excess oil in skillet.
Add remaining 1/2 Tbsp oil to oil in skillet (there should be about 1/2 tbsp left after searing beef), reduce burner to medium. Saute onions and celery 3 minutes, add garlic saute 30 seconds longer then add in tomato paste and cook, stirring constantly, 1 minute.
Pour 1 cup beef broth into skillet along with Worcestershire, soy sauce, thyme and rosemary. Add potatoes and carrots over beef layer in slow cooker, then pour broth mixture in skillet into slow cooker along with remaining 2 cups beef broth. Season lightly with salt and pepper (add more to taste at the end). Cover and cook on low heat for 7 - 8 hours.
In a small bowl whisk together cornstarch with 1 1/2 Tbsp cold water until smooth. Pour into slow cooker and gently stir, cover and cook on high heat for 20 - 30 minutes until thickened slightly. Stir in peas and half of the parsley. Serve warm garnished with remaining parsley.
To prep this stew in advance: Cut up beef, onions, carrots, celery and garlic the night before cooking (and store separately in the fridge. Wait to chop potatoes so they don't brown). This will give you a huge head start the following morning because this recipe does have a lot of prep work.