Melt the dairy‑free butter in a large pot over low heat, then add the marshmallows. Stir slowly until completely smooth and glossy, about 5 minutes.

Remove from heat and stir in the vanilla and salt. Fold in the crispy rice cereal until every piece is coated.

Scrape into a parchment‑lined 8×8‑inch pan and press into an even layer with a buttered spatula, being careful not to pack it down hard.

Let cool at room temperature until set, 30 minutes. Lift out, slice into 12 squares, and serve.