Bring a salted pot of water to a boil. Peel and cut potatoes into thirds and boil for 15 minutes. Drain and mash. Let cool.
Finely chop the onion and shred the lion’s mane by pulling apart into little pieces or using a food processor.
Heat a large skillet over med-high and add half the lion’s mane to dehydrate. After a couple minutes stir then put pressure on top of the mushrooms by pressing a similarly-sized pan on top to help release moisture. Add the remaining mushrooms to the pan and press down on the top pan. Cook down for about 15-20 more minutes, stirring every so often. Remove to cool in a bowl.
In the same skillet, heat 2 tablespoon olive oil and cook down the onions for about 5 minutes, stirring occasionally.
Toss in the onions to the bowl with the lion’s mane and coat with the flour, salt and baking soda. Add the mashed potatoes, cheese, chives and dill then stir to combine well.
Beat eggs and stir in buttermilk in a separate small bowl then combine with the lion’s mane/potato mixture.
Heat ¼ cup oil over med-high in the skillet. Once hot, use a spoon to scoop and drop a heaping dollop of the mixture in. Let fry for a minute then use the back of the spoon to spread and flatten out the mixture. Cook for another couple minutes then flip and fry 2-3 more minutes on the other side.
Remove to a paper-towel lined plate and repeat until all the mixture has been cooked into boxties (~10 total). Serve warm on their own or topped with aioli or sour cream. Garnish with chives and dill.