Bring a large pot of salted water to the boil. Once it reaches a rolling boil, add cauliflower florets. Boil for 5-7 minutes until tender - but not soft. Drain cauliflower, place in a baking dish and set aside for later.
In a saucepan over medium heat, melt the vegan butter.
Add flour then stir to combine well. Cook for 1 minute and then remove from the heat.
Gradually add the milk to the pan with butter and flour, stirring well between each addition. Once the milk has all been added, place back over a medium heat.
Add the nutritional yeast and the vegan cheese (if using), and continue stirring the mixture until it has thickened. This should take about 5 minutes.
Taste and season with salt and pepper.
Pour the cheese sauce over the cauliflower florets in a baking dish - make sure all the florets are covered well.
Sprinkle over additional vegan cheese if using followed by the roughly chopped pistachios.
Place in the oven and bake for 25-30 minutes or until bubbling and golden on top.
Remove from the oven and serve!
