Line an 8x8 or 9x9 pan with parchment paper and lightly grease it. Melt vegan butter in a large pot over low heat. Add vegan marshmallows and stir until completely melted and smooth. Stir in vanilla extract.
Add rice cereal and mix until fully coated.
Press mixture into prepared pan gently and evenly.
Let set at room temperature.
Drizzle melted white chocolate over the top. Let set fully before slicing into squares.