Put about 1 inch of water into the bottom of a double boiler and bring to a simmer. Meanwhile, put the butter in a 1-quart saucepan and heat just at the bubbling stage for 1 minute over medium heat. Remove from the heat and skim, then return to the lowest possible heat to keep warm. Over medium-low heat, whisk together the eggs, lemon juice, salt, and pepper in the top of the double boiler until the sauce begins to thicken, about 3 minutes, taking care not to let the water bubble up enough to touch the bottom of the upper pan. Whisking constantly, drizzle in the butter, continuing to whisk to a smooth, creamy consistency.
