Preheat the oven to 225°. In a large skillet, melt 3 tablespoons of the butter. Add the shiitake and cook over moderately high heat, stirring occasionally, until golden, about 7 minutes. Add the shallots and cook, stirring, until softened, about 3 minutes. Add the pea shoots, season with salt and pepper and cook just until wilted, about 1 minute. Keep warm.