Steam half a head of cauliflower until soft when poked with a fork (about 5 to 8 minutes). Drain the cauliflower and set aside to cool.
Peel the parsnips and slice them thinly using a mandoline slicer or simply slice them very thinly (and carefully)with a sharp knife.
Over medium heat, sauté the sliced onion in a couple teaspoons of oil until fragrant and beginning to turn translucent, about 5 minutes.
Once the cauliflower is cool, combine the steamed cauliflower, milk, flour, salt, nutmeg and thyme in a blender. Blend until combined
In a well buttered 9” x 13” casserole dish, lay down slices of parsnip, completely covering the bottom (it’s okay to overlap slices). Layer a third of the sauteed onion on top, sprinkle with cheese, and spread 1/3 of the cauliflower mixture over the layer. Repeat this process with the remaining parsnips, onion, cheese, and sauce, with a sauce and cheese layer on top.
Original recipe from Feasting at Home: http://www.feastingathome.com/2012/11/parsnip-gratin-with-gruyere-and-thyme.html
*or use full-fat canned coconut milk