Grease an 8x8 baking dish with coconut oil or vegan butter. Set aside.
Melt the vegan butter in a light-colored large pot (so you can see the change in color) over low to medium-low heat. Once it melts, it will foam, and then turn a light golden color. Stir frequently and keep your eyes on the butter so it doesn’t burn.
Once the butter starts to brown and smells nutty, turn off the heat and add in the marshmallows, vanilla extract, and a pinch of salt. It should be hot enough from the butter to melt the marshmallows, but if necessary, turn the heat back on low until the marshmallows are melted.
Remove the pot from the stove and stir in the crispy cereal until just combined. Move quickly to transfer the rice krispie treats to your prepared pan.
Gently press the cereal mixture into an even layer with your fingers or use the paper wrapper from the butter. If you pack them in too tightly, it makes them hard instead of light and airy.
Let cool for about 30 minutes at room temperature. Run an offset spatula or butter knife around the edges of the pan to loosen the rice krispies until they come out (you may have to invert the pan to help release them). Use a serrated knife to cut into your desired number of squares.