Prepare your 9x13 pan either by lining with parchment paper or lightly buttering. For thicker treats, use a 9x9 pan.
For easier melting, prep your marshmallows by cutting them in halves or in quarters. Or you can use mini-marshmallows as well.
Put the vegan butter in a large pot over medium-low heat.
Once the vegan butter is melted, add the marshmallows to the pot. Stir continuously with a wooden spoon until the marshmallows melt and are gooey. Make sure you don't brown the butter or marshmallows.
Remove the pot from heat and add the vanilla extract. Stir well.
Add the 5 cups of crispy rice cereal and stir until well combined.
Scoop the cereal mixture into the prepared pan. Use a piece of parchment paper on your hand and press to flatten out the mixture.
Allow to cool for 20 minutes before cutting into squares.
Store in an airtight container at room temperature for up to 3 days.
Notes
If you are using full size marshmallows, cut them into pieces so they can melt easier.
Do not let the vegan butter burn. You won't get "brown butter" like regular butter. Instead you'll get unpleasant treats that will need to be thrown out.
My favorite brand of vegan marshmallows is Dandies.
I like using Country Crock Plant Butter in sticks in my desserts.