Ingredients :

• Semi-salted butter — This is what makes the flavor, really everything. No question of using unsalted butter here — the salt in the butter creates that sweet-salty contrast that makes the cake addictive. Use good quality: Bordier if you want to treat yourself, Paysan Breton otherwise. Most importantly, take it out of the fridge at least two hours before starting.
• Egg yolks — Five yolks for a single cake is a lot. But that’s exactly what gives the crumb its golden yellow color and its fatty richness in the mouth. Keep the whites in the fridge — they make excellent meringues or an omelet for the next day.
• Flour — T45 or T55, nothing special. Weighing it correctly really changes the result: too much flour and the cake turns into a dry brick. Sift it if you can; it incorporates much better into the dough.
• Vanilla sugar — A store-bought packet works well. If you have pure vanilla extract or a bean, it’s even better — synthetic vanilla is less noticeable in a cake so heavily loaded with butter.