In a large bowl, sift the flour, salt , cocoa powder and baking soda, then mix them well with a spoon. Set aside.
In the bowl of a stand mixer, whisk the butter, oil, melted chocolate and sugar until creamy.
Add the egg and vanilla and whisk more.
In a big cup, mix the buttermilk and vinegar with a spoon.
Pour both flour and buttermilk mixture into the bowl. Mix well until smooth (don’t over mix it).
Pour the batter in a greased 7 inch springform baking pan.
Bake in a 350 °F preheated oven for about 25 to 30 minutes.
Let cool completely.
Run a knife around the edges to loosen the cake from the ring of the springform pan.
Open the springform pan and remove the ring.
Place the cake on a cooling rack.
Put the cake upside down.
Pour melted chocolate on top and spread it around the edges.
Garnish with chocolate sprinkles.
Let the chocolate set.
Enjoy.