Heat oven to 400°F. Line 12 muffin cups with paper baking cups or grease. In small skillet, cook onions in margarine until tender. Set aside.
In large bowl, combine all-purpose flour, rye flour, sugar, baking powder, salt and caraway seed; mix well. Add milk, eggs and cooked onions; stir just until dry ingredients are moistened. Fill paper-lined muffin cups 2/3 full.
Bake at 400°F. for 15 to 20 minutes or until toothpick inserted in center comes out clean. Immediately remove from pan. Serve warm.