Butter a cake tin and add some flour. Tap that around, so that the whole tin is covered and afterwards tap out the excess.
Bring some water to the boil and pour that over the currants.
Chop the walnuts and roast them on low heat on a dry pan for about 3 minutes until they smell a bit nutty.
Add butter and sugar in a bowl and mix with the mixer for about 3 minutes until the mixture is airy.
Add the salt and the eggs, one by one, while you still keep mixing. Add the following egg, when the previous one is fully incorporated into the batter.
Put the mixer speed on low and add the flour. Stop mixing when the flour is incorporated in the batter.
Add the granola and swirl with a spatula through the batter.
Pour the batter in the buttered tin and bake for an hour until it's done.
Let it cool down for 5 minutes and then release the cake from the tin.