How to Make It
In a very large skillet, melt 3 tablespoons of the butter in 2 tablespoons of the olive oil over moderately high heat, swirling, until the butter is golden, about 2 minutes. Add one-third of the shallots to the skillet and cook, stirring, until softened, about 1 minute. Add one-third of the mushrooms and cook, stirring occasionally, until tender and golden, 5 to 7 minutes. Add one-third of the pickle brine and cook until absorbed, about 1 minute. Transfer the mushrooms to a serving bowl and keep warm.
Repeat the process 2 more times with the remaining butter, olive oil, mushrooms and pickle brine. Season the mushrooms with salt and pepper and serve.