In large skillet over medium heat, cook and crumble ground beef, onions and Italian seasoning until no longer pink; drain. Stir in pasta sauce and tomatoes. Set aside.
In medium bowl, combine ricotta cheese and egg; set aside.
In slow cooker, layer ? sauce, 1/3 pierogies, ? ricotta and ? cup cheese. Repeat layer, ending with pierogies, sauce and 1 cup cheese.
Cook on HIGH 2-2 ? hours or LOW for 4-5 hours; do not stir.
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