Prepare the Meat: Cut the stew meat into 1-inch cubes, discarding any large pieces of fat (marbled fat is fine). Sprinkle the beef with black pepper, garlic salt, and celery salt. Toss to coat. Sprinkle the flour over the meat and toss again to coat evenly.

Brown the Meat: Heat 3 tablespoons of olive oil in a large skillet over medium-high heat. Add the beef in batches, avoiding overcrowding. Brown each side for about 45 seconds. Add more oil if needed. Transfer the browned meat to the slow cooker.

Cook the Onions and Garlic: Reduce the heat to medium and melt 1 tablespoon of butter in the same skillet. Add the diced onions and cook for about 5 minutes until softened. Add the garlic and cook for 1 more minute. Splash in a bit of wine to deglaze the pan, using a silicone spatula to scrape up the browned bits. This adds great flavor to the stew. Transfer the onion and garlic mixture to the slow cooker.

Add Remaining Ingredients: Add all the remaining ingredients to the slow cooker, except for the peas, corn starch mixture, and 2 tablespoons of cold butter.

Cook the Stew: Cover and cook on low for 7 ½ to 8 hours or on high for 3 ½ to 4 hours, until the vegetables are softened and the potatoes are fork-tender.

Finish the Stew: Add the frozen peas in the last 15 minutes of cooking. Remove the bay leaves and rosemary stem before serving.

Optional Thickening: If you prefer a thicker stew, combine ¼ cup cold water with 3 tablespoons of corn starch. Slowly stir this mixture into the stew and allow it to thicken as it cooks. It will continue to thicken once the heat is turned off.

Add Butter for Finish: Turn off the heat and swirl in 2 tablespoons of cold butter for a smooth and velvety finish. This technique, called "Monter au Beurre," gives the stew a silky texture.

Optional Darkening: Add 2-3 drops of Gravy Master for a richer, darker color.