Cook the pierogies according to package directions.
Cook bacon in a large nonstick skillet until crisp. Remove bacon; crumble. Increase heat to medium-high. Add onion, sugar, and thyme to drippings in pan; sauté 5 minutes. Stir in peas; sauté 1 minute. Add pierogies, salt, and pepper; cook 30 seconds. Sprinkle with crumbled bacon. Serve with sour cream.