In a large, deep skillet, melt 2 tablespoons of the butter in the oil. Add the parsnips and cook over moderately high heat, stirring occasionally, until lightly browned, about 6 minutes. Add the shallots and cook, stirring, until softened, about 2 minutes. Add the stock and thyme and bring to a boil. Season with salt and pepper, cover and simmer over low heat until the parsnips are tender, about 8 minutes.