In a 5-qt. slow cooker, combine the first 11 ingredients. Cover and cook on low for 8-9 hours or until beef and vegetables are tender.
About 30 minutes before serving, place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and simmer for 15-20 minutes or until tender.
Drain. Return potatoes to pan; add the sour cream, butter and 1/2 teaspoon salt. Mash until smooth.
Set aside 12 peas for garnish.
Add remaining peas to the slow cooker. Increase heat to high. In a bowl, whisk the flour, water and remaining salt until smooth; stir into stew. Cover and cook for 5 minutes or until thickened.
Divide stew among six bowls.
Place mashed potatoes in large resealable plastic bag; cut a 2-in. hole in one corner. Pipe ghost potatoes onto stew; garnish with reserved peas.