Put a cake ring onto a platter. Make sure that the size of the cake layers is the same as the cake ring. If there's a difference, you can cut off a bit of the cake layers along the edges.
To make the cream, heat 3 1/3 cups (800 ml) of the milk that's been sweetened with the sugar and pour the starch in it, dissolved in the remaining 4/5 cup (200 ml) milk.
After it comes to a boil, beat well with a whisk. Put 1 cake layer at the bottom of the ring and pour on 1/3 of the cream. Sprinkle with ground walnuts, 1/3 of them as well.
Place the second layer on top and pour on cream. Continue in this fashion until you put on the last layer, cream and the remaining walnuts.
Let it cool for several hours before consuming. Carefully slide a knife along the inner side of the ring and remove it. Cut it into slices.