When Pierre Hermé's apprentice shared his croissant troubleshooting checklist with me, one culprit stood out: butter temperature creep. Most home bakers fold their dough when the butter is still slightly warm from their kitchen, causing it to absorb into the dough rather than creating distinct layers. The result? Croissants that puff once, then collapse into dense, oily disappointment. The Butter Temperature Rule Keep your laminated dough between 62–66°F throughout the folding process. Hermé's trick: refrigerate your work surface with a baking sheet for 10 minutes before each fold. Touch the dough—it should feel cool but pliable, never cold. If it's cold enough to crack at the edges, it's too cold and the butter will shatter instead of creating those critical sheets. "The lamination is not about folding perfectly," Hermé told me. "It's about keeping the dough and butter at exactly the same temperature so they move together as one." The final proof matters just as much. Under-proofed croissants (3–4 hours instead of 8–12) bake before they've expanded fully. Don't rush this stage. Your oven spring depends entirely on fermentation, not time alone. A cold final proof—overnight in your refrigerator—also enhances flavor and makes scoring easier.