Ingredients :

• The Lemons — Use untreated, organic lemons if possible. Not just to be organic, but because you’re using the zest—and the zest of waxed lemons has a chemical aftertaste that comes out during baking. A good lemon should feel heavy in your hand. Avoid very thick skins: they mean less juice inside.
• The Sugar for Caramel — Standard white sugar, not brown sugar. Brown sugar caramelizes differently and can burn before it’s ready. Four tablespoons isn’t much—so keep a close eye on it. It can go from golden to bitter in barely twenty seconds.
• The Butter — Unsalted butter, melted but not piping hot. If you melt it in the microwave, wait until it’s lukewarm before adding the eggs—otherwise, you risk scrambling them. Standard butter works perfectly here.
• Baking Powder — 8 grams, no more. A standard sachet in France is often 11 grams—use a little less than the whole packet. Too much leavener and the cake will puff up then collapse on itself after baking.