BEAT first 7 ingredients in medium bowl with mixer until creamy.
RESERVE 1 tsp. onions. Add remaining onions, crabmeat, and 1/2 cup shredded cheese to cream cheese mixture; mix well. Spoon into microwavable bowl.
MICROWAVE on high 3 min. or until heated through, stirring after 1 1/2 min. Top with remaining shredded cheese and reserved onion.
Serve with Ritz crackers.
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