Prepare all ingredients:

cremer the softened butter along with 2 thirds of sugar using a whisk.

Add the lemon zests. Mix well.

Separate eggs. Add egg yolks to the butter/sugar mixture,...

...continue to beat with the whisk until the preparation thickens.

Add the sifted flour to avoid lumps.

Add it quickly using the electric beater.

Beat the egg whites very firm...

...and stiffen them with the remaining sugar.

Delicately add the firm whites that are slightly meringue to the batter.

Pour the obtained batter in a silicone cake mold like "Sili Cook"...

... and bake in hot oven at 180°C. Bake 30 minutes for mini-cakes and a good 50 minutes for a large cake.

When finished, check that the cake is ready by inserting the blade of a stainless steel knife. The blade must come out dry when the cake is baked.

Remove from the mold on a cooling rack.

Leave to cool before slicing and eating.