hi, Adrienne,

I AM German and I do a lot of baking, but I had never heard of a thing called lucullus cake prior to your posting. That really made me curious and I looked it up on several german online search engines. As far as I can see there are to completely different sorts of cake. One called Lukullustorte, a sort of white cake with a fuit mousse filling, and another one called Lukulluskuchen.
In Germany the same dish often goes by very many different names, depending on the region you live, so surprise, surprise, I did know Lukulluskuchen ( we called it cold muzzle or cellar cake) from my childhood birthday parties, and it really is a classic german cake, BUT it never goes in an oven, so I don't know if this is what you are looking for. Lukulluskuchen is certainly a classic cake but has not been very fashionable for the last 25 years or so. Therefor I never made it myself, but I asked my husband's aunt Ulla, who once told me, that she had a very good recipe for it.

Aunt Ulla's Lukulluskuchen

2 eggs, lightly beaten
6 tbsp sugar,level or slightly heeped (to taste)
5 to 6 level tbsp Dutch cocoa powder (to taste)
6 tbsp milk
2 level tbsp vanilla sugar (substitute with 2 tbsp sugar and 2 tsp vanilla extract)
1 level tbsp instant coffee powder
1 tbsp dark rum (optional)

Mix all ingredients until smooth and sugar is dissolved.

Heat
8 oz coconut oil (hard white fat pressed from coconut meat) until liquid but not too hot, otherwise the egg mixture will curdle.

Slowly add oil to egg mixture, beating constantly, until completely smooth and shining.

Now you need
about 8-10 oz store bought butterkekse (2x3 inch, 1/8 inch thick rolled crunchy cookies, that taste buttery and sweet).

Line a rectangular form (8x3 1/2 inches, 4 inches deep) with foil. Fill bottom of form with a thin layer of egg mixture (thinner than cookies), cover completely with cookies, add another layer of egg mixture, that just covers the cookies and so forth (Rather like lasagna). End with a cookie layer. Cover with foil and put in the fridge until firm (overnight).

When firm turn upside down on a platter. Cut 3/8 inch thick slices and serve.

That is really a very, very filling cake. It is actually like I remember my mother making it.
I don't know about food savety. Will the eggs be hot enough with the warm coconut oil?

Hope, this is helpful
Inge