Preheat the oven to 160 degrees.
Cream the butter with the sugar in a food processor, then add the egg yolks. Mix the flour with the baking powder and add it to the food processor.
Once you have combined them all together, you need to spread the dough into a rectangle tray. It will be a very sticky dough, so no worries, that is how it should look like.
Next up, take your jam and carefully spread it across the cake dough.
Mix the 4 egg whites until they form stiff peaks, then add the sugar and the vanilla essence until you get a meringue.
Fold in the walnuts, with a lot of care, so you don’t break the meringue. Spread the walnut meringue over the jam.
Bake the cake for 50-60 minutes. Check to see if the cake is done with a toothpick. If it comes out clean it is ready. Let the cake cool down before cutting it into squares and serving it.