Remove the metal cap from the glass ornament. Using a small funnel, pour 1 tablespoon of popcorn kernels inside.
Carefully place the ornament inside a brown paper lunch bag, keeping the ornament opening facing upward.
Fold the bag closed and microwave on high for approximately 1 minute, stopping when the popping slows down.
Leave the ornament inside the bag until the glass has cooled completely.
Carefully remove the ornament and gently shake out any unpopped kernels.
Replace the metal cap and tie a pretty ribbon around the neck of the ornament. Hang it on your Christmas tree.
Notes
Safety: These instructions describe the original project, but ordinary decorative glass ornaments are not microwave-safe unless the manufacturer specifically says so. The glass can crack or shatter, and a paper bag does not eliminate that risk.
Safer alternative: Pop the popcorn separately, allow it to cool, and fill a clear plastic ornament with pieces small enough to fit through the opening.
Store finished ornaments carefully with your Christmas decorations. The popcorn is for decoration only.