How to Make It
Preheat the oven to 375°. Rub the cedar plank with canola oil, transfer it to a baking sheet and heat in the oven for 30 minutes.
Meanwhile, in a medium bowl, combine the garlic, shallot, thyme, olive oil, vinegar and salt. Add the mushrooms and toss to coat. Let marinate at room temperature for 30 minutes.
Spread out the mushrooms on the cedar plank and roast them until they are tender, about 20 minutes.
In a small, deep skillet, combine the butter and cinnamon. Attach a candy thermometer to the side of the skillet. Melt the butter over low heat until it registers 125°. Season the salmon fillets with kosher salt and add them to the skillet; they should be completely submerged in butter. Poach the salmon, turning the fillets halfway, until just cooked through, about 20 minutes; you may have to move the skillet off and on the heat to keep the temperature between 125° and 130°.
Transfer the salmon to a paper towel–lined plate and drain briefly. Season with sea salt. Serve with the mushrooms and lemon wedges.