Cut onions into 1/2-inch slices, and separate into rings. Set aside.
Combine 1 1/4 cups Pancake Mix and sugar. Stir together buttermilk and beer; whisk into sugar mixture until smooth. Set aside.
Place onion rings and remaining 1/2 cup Pancake Mix in a large zip-top plastic freezer bag. Seal and shake to coat.
Pour oil to a depth of 2 inches into a Dutch oven; heat to 370°.
Dip onion rings, 1 at a time, in batter, coating well. Fry, in batches, 4 minutes or until golden, turning occasionally; drain on paper towels. Serve immediately.
Kitchen Express: Substitute 1 3/4 cups all-purpose baking mix for 1 3/4 cups Pancake Mix, and omit sugar. Proceed as directed, reducing frying time for each batch to 2 minutes.