Chop the head of cauliflower into florets and put inside a large saucepan. Add water to submerge all the cauliflower and bring to a boil. Cook through for 20 minutes in total, until the cauliflower is fork tender.
Drain the cauliflower and add it to a processor. If your processor is small you may need to puree it in batches. As you pulse the cauliflower will work its way up the sides at which point you should stop, take off the lid and push it back down using a spatula. Do this 2-3 times until smooth.
Once all the cauliflower is smooth add in the pumpkin and pulse until combined and uniform in color and consistency.
Add the eggs, melted butter, erythitol, salt and vanilla extract and pulse until smooth and everything is combined.
Pour all the mixture into a 9x13 casserole dish and bake for 20 minutes.
Net Carbs (Casserole): 3.6g / Net Carbs (Syrup): 0.4g