For the crisped buckwheat, pre-heat oven to 425℉ and oil an unlined baking sheet.
In a cast iron pan over medium-high heat, toast the buckwheat groats until fragrant (about 2 minutes). Allow the groats to cool and quickly rinse under cold water. Add the groats, water, salt, and thyme to a medium saucepan and bring to a simmer. Cook for 6-8 minutes, then strain and cool under running water. Shake the grain as dry as possible and then spread on the oiled baking sheet. Toast in the hot oven, stirring occasionally until crisped through (15-20 minutes). Reserve when cool. Remaining groats may be stored in an airtight container for up to one week.
For the puréed cauliflower, add butter, olive oil and shallots in a medium saucepan over medium-high heat. Sauté until shallots are just soft, then add the sliced cauliflower, stock, cream, bay leaf and thyme. Cover and steam until cauliflower is tender (about 4-6 minutes). Uncover and reduce heat to medium, stirring occasionally until liquid has reduced to a few tablespoons. Discard bay leaf and thyme, then carefully purée using an immersion stick blender (preferred). Adjust consistency as needed by either thinning with stock or returning the purée to low heat if it is too loose.
For the cauliflower florets, heat a medium cast iron pan over medium-high heat, add clarified butter and then florets. Quickly sauté to color and immediately remove from heat. Season with salt and pepper and toss with hazelnut oil when slightly cooled. Reserve.
In a large cast iron skillet over medium-high heat, add butter and olive oil and heat until foam subsides for the wild mushroom mix. Immediately add shallots and sauté for 30 seconds. Add the mushrooms and continue to sauté over medium-high heat until they have begun to lose moisture and take on color (2-3 minutes). Deglaze with the wine and cook-off. Check for final seasoning and brighten with the lemon juice as needed. Microplane the zest over the mushroom mixture and reserve warm.
When ready to serve, microplane ¼ of the truffle and fold into the warm puréed cauliflower. Spoon the purée onto six small plates and arrange the cauliflower florets in the purée. Spoon the crisped buckwheat groats over and then the wild mushroom mix. Thinly slice the remaining truffle and tuck the petals among the mushrooms. Finish with a final microplane of zest, a drop of hazelnut oil and fleur de sel.