Combine first 5 ingredients in container of blender; cover and process at med. speed until frothy ( usually about 10 seconds).
Stir in onions.
Met butter in large nonstick skillet over medium heat, tilting pan to coat bottom;pour in egg mixture.Cook without stirring until mixture begins to set on bottom.
Draw a spatula across bottom of pan to form large curds. Continue until eggs are thickened, but still moist; do not stir constantly.