Chop walnuts into small pieces and toast them in a dry pan until aromatic. Let them cool completely.

Cream softened butter in a bowl using a whisk. Gradually add sugar in three batches and mix until creamy.

Add egg yolks one at a time, mixing thoroughly after each addition. Gradually add egg whites in three batches and mix well.

Add a few drops of vanilla oil and mix. Sift almond flour into the batter and fold gently.

Sift cake flour and baking powder into the batter. Fold gently using a cutting motion.

Add cooled walnuts to the batter and mix briefly.

Grease a pound cake mold with butter and pour the batter in. Shape the top into a dome and make a slit using a buttered spatula.

Bake in a preheated oven at 170°C for 40 minutes. Check doneness with a toothpick; it should come out clean.