Creaming method with Sugar-Butter technique. The difference with Gâteau chocolat de Nancy is that the whole eggs are beaten together before the flour is added.
When butter and sugar are creamed together, the rough sugar crystals cut into the fat, creating air bubbles that are held in by it. These small air bubbles serve as a nuclei for leavening gases, steam and heat. When adequately creamed, the entrapped air is more evenly dispersed among the fat leading to a better and more even rising.
Healthier choice: try using organic butter, sugar, flour and free range eggs.