Rinse the green beans. Place a steamer basket in a large pot with about an inch of water and bring to a boil. Steam the beans for 10 – 12 minutes, or until just tender.
Meanwhile, brush off any dirt or forest debris from the chanterelles. If they are especially dirty or have dirt trapped between the gills, use your kitchen sink spray nozzle to quickly rinse them. While washing mushrooms seems to be generally frowned on, a quick rinse is very effective. Allow them to drain briefly, pat them dry, then slice them about 1/4 inch thick.
Heat the olive oil in a large skillet over medium high. Add the sliced chanterelles. They will immediately throw off any excess liquid – the amount will depend on how much moisture is contained in your chanterelles – but no matter; it will all evaporate quickly. Stir the mushrooms occasionally while continuing to cook them over medium high heat. When the mushroom liquid has evaporated completely, continue to cook for another minute or two to brown the chanterelles slightly. Add the dry sherry and cook for 2 – 3 minutes or until the sherry has reduced to a syrupy consistency. Turn off the heat, but leave the mushrooms in the skillet for now.
Toast the hazelnuts in a dry pan over medium heat, shaking the pan constantly to prevent burning. Continue to toast the hazelnuts until they begin to brown and become fragrant. Remove the hazelnuts to a cutting board, allow to cool slightly, then chop them very coarsely. Return the nuts to the pan over medium heat with the butter. Cook for about two minutes or until the butter foams slightly and the nuts are a toasty golden-brown. Remove from the heat immediately.
Add the steamed green beans to the skillet with the warm chanterelles. Add coarse sea salt and black pepper to taste and toss together to combine. Heap the green beans and chanterelles in a serving dish, top with the toasted hazelnuts and a generous sprinking of sea salt.