Ingredients :

• Vanilla or lemon cake mix — This is the base and the secret. The mix already contains flour, baking powder, salt, and sugar — that’s why we don’t add anything else. Use a classic vanilla mix (about 500g). Avoid ‘light’ versions; they absorb butter differently and the texture suffers. Want a gluten-free version? Choose a mix specifically formulated for it, not an approximate substitute.
• Melted butter — It replaces both the oil and water indicated on the box. Melted, not clarified — the water naturally present in the butter stays in the batter and contributes to the softness. Let it cool for two minutes after melting before incorporating the eggs. Boiling butter on cold eggs will scramble them.
• Eggs — Two large eggs, at room temperature. Take them out twenty minutes before starting. An ice-cold egg in hot melted butter will seize up and create fatty lumps that can’t really be fixed. They provide the structure that allows you to cut clean bars instead of a crumbly mess.
• Sugar + cinnamon — This is the snickerdoodle signature, the essence of this dessert’s character. The classic ratio: four parts white sugar to one part cinnamon. Use Ceylon cinnamon if you have it on hand — it’s sweeter, almost floral, and less harsh than the Cassia sold in supermarkets. Sprinkle generously over the entire surface without mixing it into the batter.