Beat egg and sugar until foamy, add soft butter then flour, sifted with baking powder.
Add milk slowly, enough to have a thick dough, not too liquid.
Add pistachio cream and pistachio grain, mix well.
In a greased pan put some spoonful of dough then pour some melted chocolate.
Add more dough then chocolate until you finish both.
With a long toothpick move slightly the dough to marble the cake.
Bake at 356°F for 30-40 minutes or until a toothpick, inserted, comes out dry.
When completely cool reverse the pan, put the cake on a grill pan, pour the rest of the chocolate, melted, then sprinkle with pistachio grain.