Preheat the oven to 180 degrees C (350 F) and grease a casserole dish.
Simmer the potatoes for 10-12 minutes, and steam the cauliflower for 7-8 minutes, until both are fork-tender.
When the potatoes are cooked through, drain them and transfer to a blender or food processor together with cashews, plant based milk, nutritional yeast, mustard, cornstarch, tamari, paprika, garlic powder, cumin, garlic cloves and lemon juice. Blend until very smooth.
Now, heat the olive oil in a large pan over a medium-high heat. Add the onion and cook for 5 minutes, until softened.
Add the steamed cauliflower florets and the sauce, stirring for 2-3 minutes until the sauce thickens.
Transfer the cauliflower to the casserole dish and add the breadcrumbs on top. Bake in the preheated oven for 25 minutes, until crispy and golden brown on top.
Instructions for storage and freezing
Keep in the fridge in an airtight container for up to 3 days in an airtight container. Reheat in the microwave, or in the oven for around 10 minutes.
In order to freeze, allow to cool completely and then place in freezer bags. Keep in the freezer for up to 2 months. In order to reheat from frozen, place the frozen cauliflower in a casserole dish, add extra vegan cheese and place in the oven for 35-40 minutes.
How to make ahead of time
You can cook the potatoes and cauliflower ahead of time as part of your meal prep routine, and keep them in the fridge in an airtight container for up to 4 days. Then, all you need is 5 minutes to make the sauce, assemble the casserole, and pop in the oven.
You can also assemble the casserole together with the sauce, wrap in cling film and keep in the fridge for up to 3 days. Then, simply bake it as instructed when ready to eat.