Chocolate Sponge with layers of sour cherries and cream (Kirsch optional), chocolate Sprinkles on side, and chocolate swirls or shavings on top. 
What size do you need to choose? This depends.
If this is the only sweets you will be serving, you need a bigger cake than when you add other cakes and pastries to your catering. We recomend the following:
 
7" = for ca. 6-8 people
8" =  for ca. 16-20 people
9"  = for ca. 25-30 people
10"  = for ca. 30-40 people
12"  = for ca. 40-50 people