Hard boil the eggs for 10 minutes. Plunge into cold water, peel and retain only the yolk.
Beat the butter and sugar until creamy. Pass the egg yolks through a fine sieve, add them to the butter and sugar, and beat well until light and fluffy. Stir in the walnuts. Divide the mixture into two.
Divide the biscuits into four layers. Line an oblong tin (