Toss Stew meat with 2 Tbsp of Salt, 1/2 Tsp Garlic Powder, and 1/4 cup of flour. Make sure that meat is coated thuroughly.
Heat 3 tbsps of olive oil to medium heat. Add the meat to the heated pan. Thuroughly brown each piece of meat in the pan.
Reduce heat to medium and melt 1 Tablespoon butter. Add onions and cook for 5 minutes. Add garlic and cook for 1 minute. Use a silicone spatula to clean the bottom of the pan, removing any brown remnants. This will give the soup lots of good flavor. If necessary, add a splash of wine to help loosen it. Transfer the onions/garlic mixture to the slow cooker.
Add all remaining ingredients except for the peas, corn starch mixture, and 2 tablespoons of cold butter.
Cook on low for 7 ½ to 8 hours or high for 3½ to 4 hours, until the vegetables are softened and the potatoes are fork tender.
Add the peas during the last 15 minutes of cooking.
To thicken, combine ¼ cup COLD water with 3 Tablespoons of cornstarch. Slowly add it to the stew, stirring to incorporate. It will continue to thicken upon standing.
Turn off the heat. Remove the bay leaves and rosemary stem. Swirl in 2 tablespoons of cold butter for a smooth, velvety finish.