Ingredients :

• Butter — The base of everything. Use good-quality unsalted butter — not necessarily the most expensive, but not the cheapest either. A churned butter or AOP Charentes-Poitou gives a rounder flavor. It will be added cold, in pieces, off the heat: that’s what creates the silky texture.
• Lemon — A real yellow lemon, squeezed by hand, not bottled juice. The difference is immediate — bottled juice often has a bitter undertone that ruins everything. A medium lemon yields about three tablespoons, which is the right amount.
• Shallots — Two small ones, finely minced. They will melt and almost disappear visually, but their sweet-mild taste remains. If you don’t have any, a small spring onion can work — but shallot gives something distinctly more delicate.
• Heavy cream — At least 30% fat. It stabilizes the sauce and prevents the butter from separating when heated. Light cream doesn’t hold as well — the sauce risks breaking and becoming greasy and disappointing.