Line a 20 × 30 cm rectangular baking tin with parchment paper, leaving a little overhang at the sides if you would like to lift the cake out more easily.
Rinse the raisins and pat them thoroughly dry with a clean kitchen towel or paper towels. Any excess water can make the batter unnecessarily wet.
Coarsely chop the walnuts. The pieces should be small enough to distribute evenly through the cake but large enough to remain visible in the finished crumb.
Place the eggs and sugar in a large mixing bowl.
Beat with an electric mixer until the mixture becomes very pale and thick. Depending on the mixer, this will usually take approximately 3-5 minutes.
Sift the flour together with the salt.
Add it to the egg mixture in two or three additions, folding gently with a spatula after each one. Use broad movements from the bottom of the bowl upwards and stop as soon as no dry streaks remain.
Fold in the chopped walnuts, followed by the raisins.
The batter will become noticeably heavier once the additions are incorporated. This is normal, but avoid mixing it longer than necessary.
Transfer the batter to the prepared tin and spread it evenly, paying particular attention to the corners.
Bake for 35–40 minutes, until the surface is golden brown and the centre is set. A wooden skewer inserted into a section of cake rather than directly into a raisin should come out without wet batter.
While the cake is still hot, use a sharp knife to cut it into diagonal strips and then in the opposite direction to create diamond-shaped pieces. Allow the pieces to cool before removing them from the tin.