Cook florets in a large pot of lightly salted water 5-7 minutes, until tender. Drain; return to pot to keep warm while you prepare sauce.Place shallots, wine and 1 tablespoon lemon juice in a small saucepan over medium heat. Simmer until reduced to 1 tablespoon. Reduce heat to very low; stir in a few small pieces of butter, swirling with a wire whisk until mostly melted. Gradually add the remaining butter, whisking constantly until sauce is smooth. Season with salt, white pepper and remaining lemon juice to taste. Do not allow sauce to boil. Pour sauce over broccoli.